I would not trust the Zone recommendations. Is that -17 at your house on New Years day the low temperature, or the temperature with wind-chill?
The area around zero degrees is the critical area for Navaho and similar Arkansas blackberries. I have seen some cane die back on my Ouachita around 2 degrees. I don’t believe the publications that suggest -10 is the critical point are correct. My 0-2 degree night last year resulted in die back on a lot of the canes, but they grew back the next summer.
Chester is less sensitive to cold, but I don’t know by how much. It produces a huge amount of fruit, which is not very sweet compared to the Arkansas blackberries in my area.
I don’t have any experience with PAF.
Osage and Von are to other thornless possibilities but I have not grown them and I expect a low around zero is the cutoff
It may be useful to know which varieties that Morris Orchard and Dickie Brothers Orchard grow in Central Virginia.