Sea commander
Alan
The mfa 850 is heavy on the amps, a small 4ah battery wont last long, I personaly dont use LiPo's, I use NmHI cells, 6volt 3700mah packs coupled in series for 12 volt. Mine came from component shop but you can get them from many supplyers.
My boat is a 34" Huntsman with a Turnigy 35/42 1000kv outrunner motor. (Goes like stink!!!) it also has a water cooled motor mount
Depends if you want to change the setup you have? the Turnigy will give the power you want but you will need to change your ESC
Mark
Etherow Model Boat Club