RE: OS 46AX speed prop?
Do you mean specifically on the .46AX or in general?
Could be that they simply run up against a drag wall on many aircraft and the engine's peak horsepower is the limiting factor. I would imagine in that case the aircraft is flying much closer to pitch speed of the 10-7, and the rest of the flight behaviour (launch, vertical etc.) is also better due to the disc area and lower pitch. Unless I goofed the calc, the pitch speed of a 10-7 prop at 13,800 is 91.5 mph. Add to that the engine unloading in the air and the uncertainties of the pitch numbers and it probably all makes sense.
MJD