checking on sweet cherry grafted onto pin cherry

checking on sweet cherry grafted onto pin cherry, has anyone else tried this? I'll be amazed if the grafts survive, we've had quite a few nights below -35.. but a quick scratch test looks alive, though I guess cold damage might not appear until spring? the premise I'm testing is this european cultivar was reported to survive zone 4 winters and flower, and here I have it on a super cold hardy rootstock which could possibly provide some cold hardiness. The most likely outcome is that I'll regraft it lower where the snow will cover the branches, but just maybe these will pull through. #cherry #cherrygrafting #grafting