Yes, micro climates make all the difference. I often don't get a frost because I am on a canal when my friends in town do.

I have a Simpson stopper and while it is a very pretty tree it suckers a lot. I find it a bit of a pain to keep weeding them out of the planting bed. The suckers show up several feet away too. At first it didn't do it, but as the tree matured it started to appear.

I have three simpson stoppers growing in my yard that I bought by mistake several years ago from a nursery that was going out of business. Of the three only one is still doing well but that may be more from the fact that they rarely ever get watered except from rain then from the cold. They have been though several hard freezes including the year that we got down to 21 here without any problems. The largest of them has even fruited several times. I really couldn't tell you what cultivar they are though.

Simpson stopper can handle 20 - 22F with very little damage. They can probably grown in south Georgia if you wanted to.

Do they die back during the winter? I had one in full shade under the eaves of my house/oak tree and just transplanted it into a sunny corner of my yard in my tiny butterfly garden. Since in the garden it's lost tone of leaves and the few that remain clustered at the top are yellowish and sad looking. I haven't wanted to yank it though in case it comes back when the weather warms up a bit.

I acquired one in October and put it in-ground on the west side of my house but just on the east side of two medium red cedars, so it had a windbreak. I only protected it on one night when it got down to upper 20, the rest of the winter it has been on its own. It hasn't suffered any frost damage or lost its leaves. So I inclined to say they don't die back, but I am not sure on that.