RE: really good map site for NY state
Farm Hunter; if you're neighbours are growing Bartlet pears then you're probably in zone 5 and should be able to grow any variety. The best way to be sure is check what they're selling at the local nursery. You shouldn't have a problem.
You can mix semi and full dwarf apple trees but it isn't efficient. One semi dwarf tree may have a 20' diameter while the dwarf will only be 10'. It's best to plant dwarfs in one row and semi dwarfs in the next. The inter tree spacing will be about 10' for the dwarfs and 20' for the semi's (rough numbers).
Dan O.