Emperor I would be my first inclination assuming you are looking for a red-purple leaf selection. It tends to be a bit later to leaf out so it misses some late frosts. It holds its color well and eventually gets fairly large. Of course all of the reds can show some sunburn in alot of hot afternoon sun, but it should adapt fairly well. You will need to find a selection that shows some lower branching or it will tend to get much taller before branching out.

have u ever seen wayside gardens jm's? they are insane, you pay for em though.......

I dont have many, but fireglow is my best. It takes a lot of hot sun in my climate, much much hotter than yours. I dont know about hardiness, but all acer palmatum cultivars should be zone 6 hardy.

If the cold hardniess is a concern then how about Yasemin. Since its a purported shirasawanum hybrid it would probably be a little hardier than most palmatums. Also fits your tall growing requirement.

In any event, rather than search for one specific cultivar, Id go look and see whats available and choose from them.

'Suminagashi', 'Yezo nigishi', 'Ruby ridge' and 'Okushimo' are a few of my favorite sun tolerant uprights. 'Matsugae' is also pretty much upright and a very sun tolerant, sturdy, elegant plant.

West, it's insane to purchase JM's from Wayside. Check out Mendocino, Topiary, Eastfork, Whitman, Greer, Fairweather or even ebay.
More selection, value and cultural know how.

Here is a link that might be useful: Sources and contacts.

A couple things just about any JM can be "made" to multi low branch that mimics multi trunk so that eventually you won't be able to hardly tell the differnce. most JM's are grafted so multi "trunks" would be hard to have. Secondly you are not likely to find any JM that is totally sun tolerant if you get a summer like we had last year ...especially when young ...even my 15 year old Atros got sun damage and they were in part shade. And winter hardiness is also variable ...with siting being the most important factor ..All of the trees mentioned will do fiine for you ...One I would add that seems especially winter hardy and better sun "worthiness" than even bloodgood is the Red Baron...It also tends to branch out easily .Della still has two she is gonna get ltr this month that for some unknown reason have not been spoken for ...email her at http://nurserygirl1.tripod.com/index.html it is an exceptional tree IMHO and not well known but fits perfectly in what you are looking for ...One benifit with Della is you are getting a 4-5 year old tree which in your area is impotant to give any JM a bit of a jump start She is going the last week of this month so best to let her know soon if you are interested..David

thank you all so much for the response, i am looking up each tree completely...i am in the Boston area so my Summers arent always has hot as the more West states, plus i get a seabreeze which helps

i will post questions if i have any on this list...thank you