Nearly any RC model engine will unload between 1 and 2 thousand rpm in the air. I've had racing engines on pylon models unload 5000 in level flight, verified with an audio tach and doppler shift. But when you put an airplane into a dive, the rpm will really climb due to potential energy turning into kinetic. Many airplanes can see an easy 25% increase in speed, and thus higher engine rpm with it.

I have flown many pylon planes that were above 175 mph in level flight, so forward velocity is a larger factor with them,

On 3.0 I meant to say that the localized speed of the air changes with the change in pressure over the surface of the prop.