APC and Master Airscrew have the prop you need (Tower Hobbies) GWS has electic props (Horizon Hobbies) Look them up on the internet. the 9x4 will work. Less pitch = climb prop. High pitch = speed prop. As oohex says it it important not to overload electrics. What ever the manufacturer recommends is usually arrived at after trials at the factory. Some adjustments in pitch and diameter may be made if your trial indicates the motor and battery are still running cool and performance is not degraded.