RPM's / KV rating should depend on the size prop you want to run, and whether you are going to run a gearbox or not. If you are going to run a gearbox, then a high RPM/KV rated inrunner, like the 3200 you mentioned is the way to go, then the gearbox slows it down before it hits the prop, and you can still run the larger props. If you don't want to deal with a gearbox, then you are looking at an outrunner, and they typically have much lower RMP/KV ratings so you can just mount them to the plane, and ditch the gearbox. Typically with the outrunners, if you are thinking of running a 10x7 prop or larger, you need to stay below a 1250kv rating, for a ballpark number. Otherwise your amps are too high, and things may heat up and your flight times will be low.