Joe, if you have access to all these engines, I would setup a bench stand that would allow me to measure static thrust. Select a range of prop diameters with pitches between 4 and 10.

I would determine top RPM for each prop on each engine, Determine the static thrust of each prop on each engine. You may want to check head temp also.

Another data point would be fuel consumption, both at full RPM and at "cruise" speed.

So what eles are you going to do this summer???

Don