For brushed motors I have always used a thermometer for stock and spec, mod can be a different story as you don't always use all the power, I am not the one to be giving advice or opinions on mod however as it isn't my class of choice


This is some of the best information I have seen on here regarding motor temps, gearing and setting up you car/truck for your brushless system.
http://www.rctech.net/forum/5656941-post16.html