So, I'm tinkering with the ATtiny 3224 and its PWM capabilities. I can get 256 bits of resolution per cycle at 78.125kHz.

If I drop to 32 bits, that gets me to 625kHz, as shown in the screenshot.

I've done some searching but I may not know the right term and I'm probably looking for a rule of thumb.

What sort of resolution do you need to regulate a DC/DC switch mode? (in this case a pure resistive load that doesn't change)

I think it might be something like a factor for required percentage of change of switch ON time. Such as, you should generally be able to modify your duty cycle by increments of 5% or 0.5% or whatever for proper regulation.

Does this factor have a name?