I've always heard nema is very winter tender. I would tend to believe those sources, as none of the nurseries which ship to colder peach zones use nema. It's strictly used in warmer peach growing areas, especially CA.

Arbor day uses Nemagaurd and ships to zone 5
http://www.arborday.org/trees/treeguide/TreeDetail.cfm?id=70

:Attributes

While peach trees are self-fertile and don't require another tree to produce fruit, planting two trees is recommended for a better crop (it will still require insects to pollinate its own flowers). Fruit trees need a minimum of 6-8 hours of sunlight daily and regular water. They are not drought-tolerant. Our standard Belle of Georgia seedlings are budded to Nemaguard rootstock, and our dwarf seedlings are grafted to Prunus besseyi (Sand Cherry)

I wouldn't consider Arbor Day an authority on peach rootstocks, but of course it's your call.