None of those are the same physical size motors - TRX 3500 is 380 size (smallest), Castle 7700 is 540 size and Castle 2200 is a 1/8 sized motor (largest) and I think would be considered a 640 size. With these large motors you usually don't see a can size, they just say "large scale" when describing the size.

The numbers are the rpm/volt. If you compare equal can sizes, the motor with the higher KV number will have higher rpm at the same voltage - that usually translates to more speed. But as kv goes up torque goes down, so there's a little trade off. Castle 5700 would be slower than a Castle 7700, but would have more torque.