IDK if this has been asked before, but...

[SpEEdyBL]

It depends what speed you are gearing for. If gearing for 20 mph, sure the lower kv motor will run cooler and probably be more responsive than a higher kv motor that has to be geared way down and rev all the way up. If gearing for 60 mph, the low kv motor may never be able to get there, because it takes at least a certain amount of power from the battery (amps x volts) to do so. Lower kv motors naturally draw less amps because of their higher resistance (a 2000kv motor will have four times the resistance as a 4000kv motor of the same build), and if you try to gear a low kv motor high enough so that it does draw the same amount of amps as the high kv motor, then you will create a lot of heat because heat is resistance*amps^2.

For the in between, generally it is best to keep the rpm between 30k and 50k, which is where most motor run most efficiently; higher for high end motors such as neu and lower for low end motors such as feigao. For racing, 30-35k seems to be best for maximum runtime (not too much energy wasting just to spin the motor, and not too much energy wasted as heat in the coils)