I know of specimen trees in Iowa City, IA; Milwaukee and Wisconsin Dells, WI for certain.

There was one gardenweb member, TreeLover, that is in Minnesota, zone 4a, that claims this species has been growing just fine for him for a decade. Whether or not there is some twig dieback or it is growing into tree form there was no comment...

If I am remembering correctly, the U of M arboretum has some that look decent. Though, it looked to me, like they had suffered some damage.

I had 4 of them in NE Iowa. One winter killed or I pruned it wrong. The remaining trees are 3 years old. I hope they survive.