RE: affect of higher voltage
Ytell, one more thing. You can safely run 4S, as long as your motor and ESC are capable of running on 4S, but you will most likely need to reprop in order to keep from overdrawing your system. Changing from 3S to 4S, or 11.1v to 14.8v will increase the RPM's the motor will try to turn. Kv rating means turns per Volt, so the motor will try to turn as close to 13,320 RPM's as it can get on 4S vs. 9,990 on 3S (42-40-900Kv motor). With that increase in RPM, the power required to turn that 13X6 prop goes WAY up. You can reduce prop diameter, pitch, or both to get the current draw down to a level that's safe for your motor and ESC.
If you have a Wattmeter, you can experiment with different props on 4S and see if you can get the draw to a safe level.