Yes 4 cell is what you need. 4000-5000mah is good for most races 30-40c. Most get 230-250mah/minute so do your math to see what you need. the closer to 4000mah pack you get the more balanced you'll be on your chassis (granted your not running saddle pack set up)
Some of you running 4500mah for 10min and 5800 for 15min are getting terrible milage.