I'm really not qualified to answer your question, as I live in a zone or two warmer, but since no one else has responded, I'll offer the following info.

This is a post originally written by Dave Griffin.

"Welcome to the asylum.
I've been finishing up the hurry-up, freeze-up! work and haven't been able
to get to this until now.
I have been experimenting with growing peaches and other tender fruit
trees in zone 4a, central MN, pretty intensely since 2000 and less so before
that. I am a collector, tester, grower and breeder and have an experimental,
mostly one of a kind, collection of over 350 trees. Many of these are hardy
here (I think I may now have the largest collection of hardy plums in the
US) but some are tender and would not survive without some modification to
standard "plant and wait" horticultural practices. I have apricots, sweet
cherries and European plums that fit this description but the largest number
of these tender trees and the most tender of them are the peaches. Still, I
have been able to test around 85 named cultivars and have around 55
survivors currently, both named and private selections. They are growing as
branches on 45 hardy peach seedlings that are offspring of the Bear Creek
Siberian C based material, which are also the basis for my testing and
breeding. (Some of you have contributed material for testing or have
provided information that has helped me to track down promising material and
I am grateful.) I know that growing the test branches is not a true measure
of absolute hardiness but it gives me an indication of relative hardiness.
If a cultivar survives as a branch then I make up trees to plant out for a
second test, if not, I am through with it.
Meanwhile, the branches provide me with breeding material which I use to
make crosses on the better selections of the seedlings. Breeding trees have
been selected based on fruit size and quality and on early ripening, which
is important for hardiness as early ripe trees have more time to harden off.
These are the seed parents for crosses made using pollen from the good
quality named cultivars with a known track record for hardiness and/or those
having a long chill hour requirement, which is linked to hardiness. For
pollen parents, I have chosen from the older cultivars of commercial and
backyard/farmers market types rather than from newer commercial ones. This
is because hardiness and other desirable characteristics seem to have become
secondary considerations in contemporary breeding programs to firm flesh and
other commercial qualities. My goal is to produce a peach that I can grow
and eat in MN rather than one that looks good on the shelf in a grocery
store half way across the country. I also use pollen from the private
seedling selections I have collected and, of course, I am making reciprocal
crosses on the good quality branches when their flower buds survive the
winter. The first planting from the crosses of selected seedlings x Harrow
Diamond made in 2004 were grown out this year. They made around 3' of growth
and should provide a small amount of first fruit for evaluation in two more
years.
Here are some things I have learned, many the hard way, about growing
peaches in a cold climate:

1. Hardiness is much more complex than minimum winter temps. Especially
   so are the conditions in the fall when trees are going dormant, which is
   almost never given the attention it deserves and may be at least as
   important as winter minimums. Many trees thought to have been killed during
   a late Jan/early Feb deep cold spell may have already been dead from a
   sudden change to cold in Dec/ Nov, even though the temps were less severe.
   Of course when they don't leaf out in Spring the mid winter cold is blamed.
   Last years minimum was only -23 F with good snow in late Jan, which should
   have been easy for my trees, but we had sudden unusually cold temps for a
   long period in December before there was snow cover and so there was a lot
   of damage and mortality in the peaches.
2. The weak link in peach tree hardiness is the trunk. A tree goes
   dormant from the top down and the last thing to harden off is the trunk. An
   early cold snap that comes in before the trunk hardens off can kill the tree
   trunk without damaging any other part of it. I have learned to delay
   celebrating tree survival in spring beyond an examination finding green twig
   cambium right out to the tip of every branch and plenty of live buds. Too
   many times I have seen those buds break into lush growth only to then stop
   growing abruptly and then dry up. This is because, as it has turned out too
   many times, the trunk was dead just above the soil line. I am experimenting
   with budding and grafting 2'-3' high on the rootstock in hopes of providing
   a hardy trunk.
3. Bailey rootstock is not the answer to hardiness problems. It may well
   be a vigorous rootstock that is itself hardier than most peaches, but it
   grows too long into the fall and induces the scions grafted on it to do so
   as well, delaying senescence. The common peach seedling rootstocks Lovell,
   Halford and Nemaguard also have this effect, as does Pumiselect and the
   plums St. Julian 'A' and Mariana 2624. Siberian C based peaches defoliate
   early and induce the scion grafted on them to do so when used as a
   rootstock, or at least it doesn't get in the way. Some other plum
   rootstocks including P.americana and, less so, P. bessei so the same. I am
   experimenting with various cherry plums as rootstocks for peach with this in
   mind. Scion overgrowth? Sure, but the tree will probably be dead from other
   causes before this becomes a serious problem and staking is easy. Suckering?
   Its easy to cut off the suckers. An additional benefit of using plums is
   that you can then grow peaches in heavier soil than you otherwise could.
4. Warm wet weather in fall trumps rootstock in the battle to get the tree
   to shut down. Tarping off the roots seems to help but sweating and the
   continual presence of the tarp does not permit drying out of the soil
   between rains. I wish I knew how to do this without having to roll the tarp
   up in good weather. Anybody?
5. Southwest injury is a big problem. For those who are blissfully
   ignorant of SW injury, here is the story: its a cold day in January with
   high pressure in control. There is only a light breeze and a few white puffy
   clouds in the the clear blue sky. At 2:00 PM the high temp for the day of
   minus 15 F is approaching but while the low sun angle doesn't provide much
   heat to the earth (thats why its winter) it feels warm on your face despite
   the cold. It is also warm on the vertical tree trunks and their temperature
   has risen to way above 0 F. Then the sun dips behind one of those clouds for
   just a few minutes but that is long enough to make you feel cold and to
   bring the trunk temp suddenly goes back to -15 F. Sun, shade, hot, cold...
   repeat until cambium is completely dead on the southwest side of the tree.
   Even if the tree isn't killed outright the tree is doomed because there is
   now an entry point for insects, bacterial canker, you name it. Pertinent
   contributing factors: when the weather is the coldest the sun angle is near
   its lowest, and, the farther North you are the lower the winter sun angle
   and the bigger the danger of SW injury. By all means paint the trunks white
   as high as you can reach and put on white tree wrap/guards (why do they even
   make brown tree wrap?).
6. Don't plant a tender tree in a "protected" site. I wish I knew how many
   times someone has told me about the peach that died in spite of their having
   planted it in this great warm and wind protected site right up along the
   south side of the house. Absolute cold kills peaches not wind chill unless
   you are in a prairie climate with dry snowless winters, and then that is bud
   desiccation, not wind chill. And minimum temperatures come around sunrise,
   way after any benefit from yesterday afternoons buildup of slightly warmer
   temperatures in the tree's little heat island is long gone. Once in a while
   I even hear about someone who has tried to espalier a peach against the
   south wall of a building in an effort to get it through the winter - Geez!
7. Plant your peach on the north side of a shade source - building, row of
   evergreens, etc. It should be located far enough away so that it gets full
   sun in the summer but close enough so it is in the shade through the coldest
   winter months and up to bloomtime. Tender trees can survive severe cold,
   often colder than they are rated for, if they remain in deep dormancy. I
   found that many zone 5 trees were hardy in my zone 4a temperatures when they
   survived -29 F during the winter of '03-'04. Often the zone 5 rating
   reflects a trees inability to resist de-hardening in a warm spell and/or to
   recover from it and re-harden when the weather turns cold again... rather
   than its susceptibility to cold midwinter temperatures. Winter shade helps
   keep the tree dormant during winter warm spells, delays its breaking
   dormancy in the spring, and delays bloom. In addition, no winter sun on the
   trunk = no SW injury.
8. Peaches and apricots are a good risk in cold climates. They are very
   vigorous and so recover quickly from winter injury. Since they bear fruit on
   one year old wood they are always just one good winter away from a crop. So
   for an established peach that has died back to the snowline in winter, it
   would not be unreasonable to see 6' of new growth during the next summer
   which would then bear fruit the following summer after a mild winter.
   Madison and Hardired are good choices in spite of tender flower buds because
   they are very wood hardy and the tree is more likely to survive a cold
   winter in good condition even though the flower buds may die, then they can
   produce a full crop the next year if a mild winter follows. By contrast, my
   sweet cherries need two mild winters to get fruit - one to form spurs and
   another to get fruit. Every cold climate gets occasional mild winters but 2
   in a row is rare.
9. Don't plant a peach tree thinking that at some time in the distant
   future, grandchildren at your side, you will be able to look back and fondly
   recall this day. Plant peaches like you do tomatoes expecting their demise
   and planning for their replacement. Even in ideal climates and conditions
   peaches are not an icon for longevity and for sure they are not going to be
   when you plant them on the fringes of their range and beyond. Better to
   take heart in the fact that they are vigorous and precocious (I've had a
   partial crop on peaches in their second growing season from the graft ) and
   you might get lucky for a while with a few unpredictable crops before the
   tree dies... and that they are so very good that when you do get them it is
   worth the risk and work.
10. Reliance is not the hardiest cultivar, and it doesn't have to be. There
    is a group of relatively hardy varieties, named and unnamed, that includes
    Reliance but also Veteran, McKay (at least as hardy for me as Reliance in
    flower and wood) and Madison and Hardired Nectarine (might be a little more
    wood hardy). Within this group, planting site and horticultural methods are
    much more important than which cultivar you choose to grow. The "Haven"
    peaches from MI have done well for me as have the "Prairie" series from IL
    and the Harrow varieties. 'Sunapee', the other peach besides Reliance out of
    NH, has done well as have WI Balmer, Champion, and Polly. But again, let me
    emphasize, its not which cultivar you choose within this group but how you
    grow it. Somewhere warmer than here the choice of cultivar may be enough to
    make the difference but in my location this alone is not enough as my pile
    of dead trees will attest. From what I have learned by listening to the
    problems people have growing peaches in zone 5 and even warmer, any place
    that has serious winter to the extent that they hope to have a white
    Christmas - whether they get one or not - could benefit from some or all of
    these growing principles.
11. For those of you planting seeds and making your own grafts, no one
    year old peach tree is hardy regardless of cultivar. You could get lucky
    with heavy snow cover or a mild winter but to ensure survival for the first
    winter you have to dig it up a tree and heal it in at an angle with mulch
    over the top, or protect it some other way. Any hardiness a peach may
    eventually have comes about with age and is not present the first year. I
    don't mind killing trees if I learn something from it but nothing is learned
    from losing a one year old tree.

Good Luck and remember that grow is a verb."

That was written about 10 years ago. I think in the last few years Dave was looking for natural dwarf peach trees in order to cover them with winter protection. Dave passed away in 2014.

There is nothing in the patent info, nor have I heard anything to indicate Sugar Princess is a hardy variety, but that doesn't mean it's not. It could be its hardiness is newly discovered, or your man at the high end nursery is giving you fluff. It is a California bred peach, which means they are not specifically breeding for hardiness, but some California peaches have some hardiness.

If you choose to fertilize, and don't know what the fertility levels of your soil, I would recommend a mild fertilizer (like 10-10-10) early in the season so your tree has a chance to harden off properly.

To avoid winter damage, prune your tree in the spring or early summer.

I'm not surprised your tree didn't bloom this year. The cold winter probably killed all the flower buds.