I live in USDA 7 too, and my 3 Pentas survived 2 winters in pots. In a protected place, next to the house wall. I don't know that's count or not, but the experiment continues. My plan is to plant them out when the other plants grow large enough and they can provide a sheltered place for them.
Temperatures vary from year to year, anything that might be deduced from the pentas experience depends on what the lows were during those two years. Otherwise, the maple species has long been known to be tender. And there is a limited amount of wild living material still left. So latter day introductions happening to be significantly hardier than previously is probably not something to count on.
