20% beyond (rpm) max power is max efficiency. 10% beyond that and most current is turned to heat without field weakening.
the ratio of current to heat on the run up to max power is a little more forgiving. the efficiency is usually allot wider which sounds great.
the problem is that below a couple 1000 rpms the motor needs allot of current to accelerate so more current and lower efficiency creates allot of heat.
push the motor to max power by timing 1 lap and set the gearing to the fastest lap. let the motor cool.
push the rpms up to about 20% more and the motor will cool down allot and slow a little but now you can average your time over 5 minutes and be the fastest you can be without overheating.
set the timing to take heat more heat out at that point.
maybe bump the gearing back towards lower rpm a hair to put out more power and heat and adjust the timing to take a little more heat out.
take note of the rpm you are at.
that will be peak power and peak heat that the motor can ever dissipate over a 5 minute run.
if the next track is 10% shorter take that rpm and lower it with gearing by 10%.
do not adjust the timing again.
if you remove friction or figure out a way to cool better you will be able to gear the motor to run closer to peak power without overheating. (closer to peak power than peak efficiency).
alternatively you could also over time to field weaken and run at an rpm above peak efficiency for a long track but the car wont be as punchy.
if you drive in a way that keeps you away from very low rpms and very high rpms you will avoid both areas of the curve that are below 20% efficiency which means you will make allot less heat.