like some of the people you mentioned you're missing the forest because you think the trees are blocking your view. the timing and porting of the engine have nothing at all to do with getting more speed from the same said engine, when you drop prop diameter you increase pitch to match the load on the engine so you keep the engine in its power band producing max performance. the AX torquer engines do not respond well to tuned pipes/ultra thrust/Jett stream systems but they respond to propping the same as any other engine and as mentioned above the airframe is the limitation. don't confusing propping with trying to get more RPM.

when propping always use the sum of Diameter x Diameter x Diameter x Pitch and keeping that as close as possible you'll keep the same load on the engine, and the same peak RPM. propping for RPM is a different ballgame and is engine specific.

kc