Don't underestimate the effects of diameter.
Pitch is relatively easy to guestimate - if you have two nominally similar props (diametrer, blade shape etc) then you will see approx 200rpm difference per inch of pitch.
Diameter also affects things -a bigger prop needs more torque to spin it, so again a bigger one will drop RPM. BUT it's nothing like as linear as the pitch - RPM ratio, so an experiment is all you can do.
I went up a shade under 1" in duiameter (I had way too much RPM - the engine used to be on a much heavier boat before I got it) and I stayed at 14" pitch but went from 10&1/8" to 11" diameter. Dropped my WOT RPM by about 1100. Difference was that the prop has "let go" once since. It used to do it on every other wave, which was at best tiresome!
So yes, if you have a super light boat, you can drop diameter & load the engine back up with a higher pitch thus getting more speed, althoug hslip wioll increase as the diameter drops.... (another reason why it's anything but a linear relationship). Yam used to do a series of props that were interchangeable with the "K" series that were sold as something like "speed prop".
The theory is all well & good, BUT there comes a point where it needs blade area to "grip" the water. The lighter your boat & the flatter the water you boat in, the less grip & therefore blade area it will need.
And all that before you start changing between prop genres!