I've been puzzled with this question from time to time.

There's many settings on modern ESC's, but for this question, think stock class and blinky mode (no timing).

I have two motors and two ESC's and I think I'll measure max RPM with no load with both combos and compare.

I'm just wondering if others have done the same, and what you might have found out?

Yes, but only a small amount. Almost all brushless ESCs use microprocessors, and these require a certain amount of time (called latency) to react to the incoming sensor signals and step the motor drive to the next commutation pattern. This time delay retards the timing. The higher the free-running RPM, the farther the timing is retarded.

If you're running VTA or 17.5 1s 1/12 scale, the timing isn't affected much at all. If you are running an 8.5T on 2s, then it will be much more noticeable.

Thanks.

I'm running 17,5, 2S.

I think I'll try measuring anyway, just for fun :-)

If your ESC has a setting called Throttle PWM (Pulse Width Modulation), that can affect top end, but to what extent I can't say. Higher PWM settings will deliver more RPM at the cost of higher heat in the ESC. You could try playing with that. I've messed with it on my Vipers and I can't say I've noticed much difference.

PWM is only present at partial throttle. At full throttle, PWM ceases; the appropriate motor windings are driven 100% of the time. If a particular speed control shows a difference in full-throttle motor speed when the PWM drive frequency is changed, then there is something else (probably bad!) going on.

That makes sense, thanks :-)