It is a pretty compact vine, only getting about 8' tall. Not sure it's been around long enough for many to have a good display yet but is just a sport of 'Crystal Fountain', which most consider to be a reliable and popular double flowering type 2.

I bought Diamantina from Evison after she was presented at Chelsea. The first blooms disappointed me - very different from the dramatic photo on his website. (It was changed later) Now I like the various shades of her blooms.
As gardengal pointed out, Diamantina is not a tall clematis.
After 4 years in my yard and 2 wilts she is about 1,5m
Pic from last year:
{{gwi:590165}}
Now - a lot of buds ready to open:
{{gwi:590166}}

neptune44 - thank you for your opinion & the pictures! I'd say your blooms there are quite lovely. Did you have any blooms the first year or did it take you four years to get there?

I'm planning on planting one on each side of my arbor, so maybe I need something that gets a little taller then?? hmmmm.

Really want a clematis that is very hardy for zone 5, and preferably not one you cut down each year to the ground. So something from Pruning Group 2 or 3 (I think? I'm a little new to clematises)

Do you have any other clematis that you suggest?

thegardenat, Diamantina arrived with a few buds. I waited to bloom and after that cut the stems low.
In your zone5 most clematis will grow well. Avoid florida group and probably montana.
Tall clematis in my yard are:
Group3: " Purpurea Plena Elegance, Polish Spirit, Avant Guard, Tentel, Blue Angel, Ville de Lyon
Group2:" Claire de Lune, Mrs.Cholmondeley, Snow Queen, Vyvyan Pennel. Nelly Moser, Isago
You can get information for any clematis at:
http://www.clematis.hull.ac.uk/

"preferably not one you cut down each year to the ground"
As a general rule, to get best flowering group 3 get hard pruned and group 2 don't. However, at least consider winter appearance and winter die back in choosing since you are in zone 5. I am not trying to discourage you, but want you to have full information to make your decision. IME in my garden, some years group 2 clematis get killed back to the snow line, so Mother Nature makes them hard prune that year. That means those years I don't get the early spring double flowers from the previous year's growth, and my growing season isn't long enough for 2 bloom periods, so I get single flowers on my group 2 plants in June. Also, I prefer not to have to look at dead vines all winter, which for me is more than half the year. Where I have group 2 clematis, I have placed them where don't see them in the winter or where the dead vines are camouflaged by evergreens in the same sight line. This HF Young is group 2, and I love the June flowers and healthy green column of foliage all summer.
{{gwi:265354}}From June 5, 2012

However, I am glad that this is hidden by a large snow pile for most of the winter and is on a side of the house I rarely see after garden season is done. It is just starting to sprout now. Imagine this on your trellis, with dead leaves added, from hard frost until now. If you don't mind that, then go ahead with a group 2 clematis, but if you'd rather not look at dead vines in winter and the trellis is somewhere you will look at in the off season, then either plant to prune as a type 3 or get a type 3 clematis. From hard prune, which only takes a few minutes per plant, my type 3s prune plants grow quickly to full height each year.

Neptune44 -

Thank you for the feedback. I looked last night and my trellis is about 7 feet tall. Thank you for the link. I will take a look at the tall ones you have and see if any of those would fit better. :) I am just so in love with the blooms on diamantina.

nhbabs -

Nope I definitely appreciate the info! I don't want to regret this decision since the arbor is going to be a focal point of my garden.

I actually don't mind the look of these vines in the winter too much, I realize they're probably a big eye sore for a lot of people but I left one I have spilling out of a container all winter because it was just nice to have some color - even if it was brown. :P

How often does your diamantina die back to the ground? I understand it'll happen w/ really harsh winters but I am trying to find something that can survive normal winters in zone 5.

Thank you for letting me know type 3 do get to their full size. I will have to do some thinking now.

I don't have Diamantina, but most of my early large flowered hybrids die back about half of the time. I am in the northern end of zone 5, so I may have harsher weather than yours. They all survive and regrow, no problem, just some winters there are no living above ground vines. I completely understand liking brown in the winter. My favorites are the beech trees which often hang onto their previous years' leaves until about now.

I am in somewhat southern Iowa (just south of Des Moines) so it might be a tad warmer but not a whole lot!

So you prefer the ones you cut down each year because they come back stronger, grow to their full size and bloom twice, is that correct?

It's such a dull part of the year, all that white. I sure wish I lived somewhere that didn't snow for half the year.

No, the type 3 (hard prune) only bloom once, but they do grow to their full size each year, and their bloom tends to go on for quite a while longer than any of my type 2s. I also like that they bloom midsummer when there isn't as much blooming as in spring when the type 2s bloom.

Okay thanks for clarifying. I went ahead and picked up two diamantinas today. We will see how they do!! :)