Go bonkers and do 1515 2700kv on a good 4s pack. Slap the 47T spur and make sure you have the hardend ring gears. You can also use RCM 46T delrin spur kit.
Get the Novak Ballistic 8 2650kv motor if you want to go sensored with a Tekin RX8 esc and added caps. Sensors will help if you want to start to overgear a bit.
Read here what my 4s GTP setup does--
http://www.rc-monster.com/forum/showthread.php?t=30604
6 KiloWatt A123 Racer
GTP-Pletty Big Maxximum+RX8. GTP-C50-6L Hacker+RX8. CRT.5-Pro4+ZTW esc.
24s2p EVG SX 49.6mph Ebike.
18s4p Raptor 60mph Ebike. 11.5KW