For what it's worth, the power an electic motor delivers to the prop goes up exponentially with increasing voltage. Going from 3 to 4 cells will just about double the motor's power, if it doesn't burn up first. The same prop that is a perfect match for the motor with 3 cells will grotesquely overload the same motor with 4 cells.

This is why a good amp meter/ watt meter, is a must have item for everybody who is seriously into electrics. Every time you try a different prop, gear ratio, or cell count, you need to check the amp draw at full throttle. The price of a amp meter is a bargain compared to fried ESCs and smoking motors.