Before some blow hard pipes in here are the basic facts.... Firstly this is a loaded question ask ten folks get ten answers cause there are so many variables involved... your neigbor 20 feet away may have success and you won't with the same tree. The fact is you are and will always be you are in a borderline area fgor Jm's.That doesn't mean you shouldn't grow them or can't but My suggestion , if you are just looking for a nice red Japanese maple.... get a generic seed grown Atrpurpureum type or a Bloodgood , Red Baron ( if availble) maybe Ruby Ridge ( if available),E1 or Fireglow or other such red upright spawned from the Atro. PERIOD ...I would stay away from dissectums although the Tamukuyama is the best of the lot.

That said containerizing JM's allows you to grow anything ... and if you have lots of $$$ experiment...

Most planted out Jm's "can" survive zone 5b and possibly zone 5a ( most winters) and some may thrive ... it's all in how much work and luck you are willing to do and have and whether you really want more than a basic red Japanese maple which is what 99% of folks want anyway ...David

As long as you are not prone to the huge temp swings that we get in the midwest and south east that can cause japanese maples to push growth before our last frost you may be fine with a lot of things. I would also try to plant them in areas that is protected from lots of wind.

In addition to acer palmatum 'Bloodgood' and 'Tamukuyama', I would also try 'Koto-No-Ito', Acer Robustum, any of the Japonicums such as 'Green Cascade', Shirasawanum 'Aureum', 'Autumn Moon' and Ogureyama.
Acer Pseudosieboldianaum

One other option you could consider would be the beech cultivars' Fagus Sylvatica'Ansorgei', Purple Pendula and 'Purpurea Nana'. They stay small and are likely more cold hardy.

I was also told by a maple expert years ago that I could gain 1 zone of hardiness by spray my Japanese maple with something like Wilt-proof in late fall-early winter. I have not verified this.

David

Yes I was only talking about Palmatums most Japonican's will do ok.."PROBABLY" and some Korean maples but these are not traditionally what most folks want when they ask for a Japanese Maple ...I have heard mixed stuff on Koto no ito not unlike most other Palnmatum cultivars...I think my above post would speak to that...
As far as wilt pruff ..Most "experts" poo poo it and don't recomend it's use and since I have seen no studies i think it is perhaps AT MOST of some but likely limited usefulness and perhaps totally useless who knows ...I certainly wouldn't propose it as a zone pusher until there was scientific proof...And with so many variables, as i said above, in real world usage, one could be easily fooled as too it's usefulness ...I see it more as a plecebo for the owner to make them feel they have done all possiblre things for success. But Then I am no expert on Wilt Pruff ...these are just what I have read and observed...I think if it were Nirvana for zone busting everyone would be using it and it would be widely available and promoted which it ISN'T...David

My suggestion is to grow whatever cultivar you please among Acer Palmatums. Last year we did much better than those in traditional Japanese Maple zones with the area south seeing hot March temps followed by a bitterly cold April. Here, at least in the northern suburbs of Chicago we had cool temps that then warmed up in April like normal.

I am in the process these past few years of trying to grow whatever cultivar I see as nice unless there is direct evidence of it not being able to grow here, or if it fails here. In many posts we have had here and in other posts most all cultivars (at least the most popular) have been successfully grown in this zone.

I used to think that only a few select ones (i.e. Bloodgood, Crimson Queen, Red Emperor) did fine here. But after planting different cultivars and learning from others that they have and continue to grow many varieties of Japanese Maples I've come to the conclusion that "the shoe is on the other foot," that is, unles proven otherwise GROW WHATEVER CULTIVAR YOU WANT.

However, just remember, nothing here will grow as full or big as say in the Pacific Northwest. Mine are wimpy compared to my parent's garden in Seattle. Also, my longest lived tree of five years, a Crimson Queeen, has not grown very much sisnce I planted it. However, many laceleaf Maples do well here. And, try to keep your JM's enclosed and protected by a hedge, a fence or barrier from open wind.
Microclimates are very important.

As I've done in other posts I will keep readers updated on what has done well, and what hasn't. I'm waking up from hibernation! It's been a long winter, and I'm finding that in the past couple of years rabbits do much more damage to my small plants than the cold due to the prolonged snow cover. More reason to get bigger trees! Those fared better becasue the branches were not reachable. Anyway more on this later since the ground is still frozen with snow.

Here are some links from past discussions here that goes into more details. I hope this helps:

http://forums.gardenweb.com/forums/load/maple/msg0812304332640.html

http://forums.gardenweb.com/forums/load/maple/msg0912365414406.html

http://forums.gardenweb.com/forums/load/maple/msg0618582215394.html

http://forums.gardenweb.com/forums/load/maple/msg072132559023.html