KV rating is essential the RPM rating of motor. It's supposed to be how many RPM a motor will spin at a given voltage.
RPM is only half of the power equation though. power=RPMxTorque
(keep in mind these ratings are generic to make an example).
Say you have the following motors, all the same turn.
Motor A 2200 KV
Motor B 2250 KV
Motor C 2500 KV
Motor D 1950 KV
However
Motor A 8 oz Torque
Motor B 10 oz of Torque
Motor C 4 oz torque
Motor D 16 Oz of torque
As you can see, Motor C might make a ton of RPM, but it doesn't make very much torque....while Motor D makes a ton of torque, but a lot less RPM. Motor B is pretty stout in both...
If you have motors with identical KV, then the highest torque one is going to make the most overall power, and vice versa.....if they all make the same torque, then the highest KV would be the most powerful.
Everything in a motor is usually a trade off....you give up RPM for torque or vice versa.....power is power, then you just gotta gear it.
KV is a stupid rating that came along with brushless motors. While I understand why we went brushless, why we gave up the standard of showing motor power output in watts is beyond me.
Later EddieO