Most websites of electric motor manufacturers have a FAQ section. Anyways, the higher the turn the more torque, the lower the turn the more rpms. Lower turns eat more battery. Then there are brushless motors. Novak, Hacker, Aveox, and Lehner are just a few companies who make them. These are the best IMO. They are virtually maintenance free, you have have to keep the bearing(s) oiled. They have the most power and are very efficient. I have one in my TC3 and one in my RC18T. Super fast! Here is a website to help:
http://www.rcboataholic.com/motors.htm