Tony brings up a good point that you probably need to help some of these hybrids and cold hardy kakis along for a few years to build up their cold tolerance. I've planted Korea Kaki for the past two winters, left them unprotected, and both times they died.
I also think it's important to keep in mind that all grafted persimmons come on seedling rootstock. There's a lot of variability in how cold hardy those rootstocks are too. I've had some American persimmon seedlings have a lot of die-back here in zonee 6. So if you can, I think it's best to grow out rootstock for yourself and graft whatever you want on it, or do what Tony does and bury the graft union below the soil.