I'm sure some folks here will have suggestions, but by and large there is not as much variation in bud hardiness and flowering times in peaches as some might lead you to believe.

Bottom line, select according to performance in your area and for taste. Then, figure out what you need to do to get a crop (build a greenhouse, high tunnel, or other method of covering/protecting blooms during late frosts). In zone 6a bud hardiness should not be a problem most years for you, but if you are like most of us east of the Pacific Coast, late frosts will be.

Good luck