In order of hardiness I would say

1. Acer psuedosieboldianum
2. Acer japonicum cultivars - Aconitifolium is great and Green Cascade
3. Acer shirasawanum - Autumn moon and Aureum are great
4. Acer palmatums like - Emperor I, Bloodgood, many of the mounding ones have stood up well like Red Dragon, Viridis, etc. Also seed grown species palmatums are supposedly tougher as a general rule (at least that is what I have been told)

Much of the hardiness issues depend on what time of year the leaves emerge. Some varieties break bud earlier and therefore are exposed to a severe frost which then kills them. Most of these maples don't like strong wind, especially when their leaves are new. So the trick with them in this zone is siting them where they are protected from the strong winds and also a site which doesn't get too much sun or warmth to early in the season. Mulch well for the winter to help insulate their roots. There are quite a few people on this forum that grown them here in Z5 that can give plenty of recommendations on the palmatums which have or havenÂt worked for them. Do a search on this forum for more lists.

Willis

If you are purchasing small plants using something like Wilt-proof might help them get established. Then again you are on the northern limit so the wind may always be a limiting factor. David

You might want to look up acer Robustum. I have seen it and the stems are much thicker than typial acer palmatums which may make it hardier. I think you can get it in a tube from forest farm. David