How many watts are you asking that little 5" prop to absorb?
It's an 1850Kv motor and it draws about 210watts at full power, which I rarely use. Mine is an APC. The 7x5 prop, recommended for the motor, is more like 280 or 300watts.
I was out flying with my 1600MaH battery today, instead of 2200. It moves the CG back at least 1/2" and reduces the AUW by 1.5oz to 29oz. Much better pitch control and tighter turns now. If I point it straight up and reduce the power, it still stalls with a flop over forwards rather than slipping backwards. Flying inverted requires just a light touch on the down-elevator to keep the nose up.
Waterproof - yes! I'm coming to the States over Christmas so I'll buy some Corrosion X that you guys always recommend. The stuff I know of in England is not very user friendly. I tried Vaseline once and burnt out an ESC with it.