your qwest for speed can be delt with by a 2s lipo or even a 3s lipo something around the 4000 to 5000 mah with at least a 25 c rating. also gear it accordingly so your not getting the motor to hot and pushing your lipos to hard.
next best tires for dirt? are you talking for racing? i would recommend proline caliber m3s, holeshots m3s, these are going to work just about anywhere even clay surfaces. hope this helps