Go for the MaxAmps 5000mAh 3s pack - fits perfectly on one side of the buggy. Pair that with a motor around 3000kv and you'll be all set for a ~40mph gearing with either 16/46 or 17/46.
Go for an L size can - the crt.5 is not a light buggy for it's size and you'll appreciate the punch.
Check out my setup - temps are really good and performance rocks!
http://www.rc-monster.com/forum/showthread.php?t=7478
Runtime bashing will be easily 20 - 30 minutes.