10xl buggy/truggy
 

lets just say if i were getting either a buggy or tuggy could a 10xl on 4s work for mild racing, could it be geared enough to be competitve mainly against nitro, i ask because i have one and i have a hacker maxx motor with no rotor but that motor gets pretty hot

running a bk 9920 what is a decent external lipo cut off i can use

The 10XL should be fine on 4s in the truggy. In the buggy, the motor may not have enough load on it causing it to heat up more. It isn't a very high quality motor, so expect it to heat up under race conditions. Use BrianG's calculator to figure out the gearing:
http://www.scriptasylum.com/rc_speed/_top_speed.html

10XL on 3S could even be good... Last week @ the track just for giggles, I ran my 12XL on 3S and I actually did pretty good.. it was a lot more controllable then when it's on 6S.. but 10XL and 4S should be pretty good i think... I'm running a 22T pinion/46T Spur...