In most radios EPA can be set to >100%.

Normally I set the EPA to 100% when mapping the throttle range in the ESC.
Would I get higher throttle resolution if I map the 120% my radio supports to the ESC's full throttle range ?
(whether the increase in resolution would actually be noticeable is a different matter )

Great question. I am also curious about this.

I doubt it. Wherever you set the EPA and subsequent esc calibration. 50% throttle on the trigger is still 50% throttle to the esc as would be 75% etc. That's how I see it. In order to change that you'd need to change the exponential setting on the Tx.

The higher you set your EPA the longer or wider the curve is. It will not change the end speed. It just dictates how wide the throttle curve is.

Yes, and maybe. There will be a higher number of counts inside the microprocessor for the input pulse width change from neutral to full throttle. But that may not result in higher resolution of the PWM drive to the motor, as the PWM might have less resolution than that used for the input pulse measurement.

To both:
I'm not talking about changing the end-speed, I'm talking about the resolution.
Going from 0 to max in 100 steps is less sensitive than going from 0 to max in 120 steps.

So how do I figure out the resolution of the ESC ? I've never seen that mentioned in the manuals

Yup, that is definitely not in the ads or documentation. The best way would be to get a copy of the ESC source code, a debugger for the microprocessor used, a logic analyzer, an oscilloscope... and by that point, you could have written your own code from scratch.

We haven't mentioned yet that if you are using a digital radio (and who isn't these days?), there is a small possibility that the resolution of the entire signal chain could be limited by the radio. But my guess is that the PWM algorithm or hardware in the ESC is the limiting factor, especially given the trend toward ever-higher drive frequencies.

P.S. All of this may not matter if you drive like me, with your trigger finger shaking.

Oh for me it absolutely won't matter to my driving, it's just stuff I was wondering and when I do that I just *need* to find out

I remember reading a thread on the subject. If I remember correctly Castle said their controllers had 1024 steps in each direction.

Futaba a long time ago, early '90s maybe, advertised 1024 step radios with some of their early digital units, and I think servos. Believe I saw an ad for some of their newer servos a while back claiming higher resolution, 4096 seems to come to mind, but I'm not sure.

I suspect most any decent equipment has well over 100 steps, but again not positive.

I have one of those radios sitting here. They were awesome back in the day.