If you want to push the northern limit on paw paws; then a least use selections from Corwin Davis(deceased) of Michigan: the pawpaw guru of Nafex for many years. If I recall correctly, from 35 years ago, two of his named selections were Sunflower and Taylor2. Michael McConkey of Edible Landscaping Nursery would have these and possibly others that may be as hardy. The person currently the most in the know on paw paws is Neal Petersen of the Wash DC area. I think paw paw native range goes up into NW NY state, John Campbell of Northern Nut Growers Assoc., is from that area, and has paw paws collected from that area. Bill McKently's Nursery of Pottsdam, NY, is always pushing hardiness frontier for fruits and nuts, so check with him.
In my experience with oriental persimmons at the northern edge of hardiness in zone 6, It was getting the grafts through the first few years and then they were ok, there are 50 year old trees growing in this area , but now we are almost zone7 in SEastern PA, so they should be much easier to establish. Try wrapping the trees with breathable protection/ insulation to cut wind dessication and rapid temperature fluctuations. In my area a commercial fig grower uses shade cloth to accomplish this on mature fig trees/ bushes.
Dan Lefever
SE PA
zone 6b - 7b