II agree, the hardiness ratings ive seen for P areosulcata is something like, -28C - about -32C. Im assuming this is what kills it roots and all, not just leaf damage, leaf loss, and top kill ( should be different temps if im not mistakin). I wont know 100% till I try for myself. A premature guess is that ill have very silimar resuts as you, although the question for me is, will it get top killed, or leaf burn/drop like yours?
Update on a few things too, the passiflora has been frozen, an has finally died back. IT took rain then snow and freezing temps to finish it off. Temp wise were fairly average for night temps, but daytime highes were a bit above average for november, seemed to have averaged out now. IF we get this "typical" winter we are being forcaste to have, a few nights below -25C ( mabey a weeks worth give or take), and -5c for a high. the best is, so far weve gotten somewhat deccent snowfall ( after the wet snow we had melted, then froze

), and average snow fall here is 2-5 feet, plenty of insulation..
Paul isnt it a bit late for your first har freeze? Your average first frost date is the end of september isnt it?