I always heard it was 300 RPM, but no matter. Are you mostly talking about 2 strokes or 4 strokes? Or both? I don't think you can come up with a rule of thumb for 4 strokes where they aspirate efficiently in the air. By the time you test fly it, land and tweak, and take it back up to confirm there's no telling what how rich you are past peak unless you are using telemetry and using the same engine heat levels.