Hope this helps.
The Kv is simply the RPM the motor will spin (unloaded), given one (1) Volt. Meaning, if the motor is a 1000Kv motor, then if a voltage of 10V is applied, the motor will spin 1000 RPM/V x 10V = 10,000 RPM.
The efficiency is the propeller blade, motor, and ESC all in...