Broadly speaking, you gear for a certain speed with any given setup- 'best' gearing gives you the speed you want & the temps stay in check; whether thats 40 or 60mph depends on what you desire. If you enter your setup info into BrianG's brilliant calculator it will spit out a pretty accurate speed estimate, just play with your spur/pinion options to get the result you want:
http://www.scriptasylum.com/rc_speed/_top_speed.html
As for temps:
Motor = 180*F maximum, ideally 120-160*F
ESC = about the same^
Lipos = 140*F maximum, ideally 100-120*F
4s & the 2200kv motor will be fine for anything upto about 40-45mph I'd say, how heavy is your truggy rtr & what lipos are you using?