This a really good question. I'm a bit of a nerd also, so when I did my E-Revo I slathered the RCM heat sync with cpu thermal paste. Didn't even think twice lol.

Anyway, I'm probably geared wrong as the esc and batts are getting barely warm, but the motor gets to about 70C after about 5 min of race style driving. The bottom part which is uncovered by the heat sync is much hotter than the actual heat sync itself.

The RCM sync is REALLY snug tho. I took it off after the first few runs to make sure there weren't any air bubbles and found that it was fine; I only put a very thin coat of paste on so was quite happy.

CPU paste isn't generally rated much above 60C tho, so I'd imagine that mine will be useless in another few runs; it'll all harden up and stop conducting the heat away from the motor. Might see if I can find some non cpu paste.