1) get a temp gauge, perfectly safe temperatures for the motor/esc will strip fingerprints off and give you a nasty burn.
2) with the stock spur, I'd be looking at a 18/19/20 Ish range. Dependant on circuit. Currently running a 22 Ish on a 6.5, but quite a tight indoor circuit.
3) check nothings binding, I pushed a motor from 70-80 degrees to 130 by over-tightening all the gearbox screws
4) get a temp gauge, seriously, your thumb is a carp temperature gauge.