Zone 5 is listed as the lowest zone for hardiness for those based on in-ground planting, meaning if you get a real Zone 5 winter, it would die back to the roots and resprout from there - and in the case of peaches, they are often grafted on some other root stock which usually gives it that kind of hardiness in the first place, and what may resprout is some wild awful tasting peach. LOL We container growers always like to give ourselves at least a zone or 2 margin to avoid alot of the major protection machinations.

You could try it and really really wrap it - maybe put a chicken wire cage around it and fill with leaves or perhaps foam peanuts or something and make sure they stay in a protected corner (and pray for mild winters...LOL). I think once these types of plants get established (usually about 3 years), they develop their full hardiness.