can I get any ideas about prop size?

[fishez4alivin]

I have a 1976 20 MA with the big enclosed head center console, also have new coating of Micron bottom paint, no t top, but a tower for antennas and radar dome, I have a 150 Evinrude Ficht with a 14 1/2 x 19 prop on it, and am only able to get 43-4400 RPMs at WOT, if i drop down to a 14 1/4 x 15 prop i should get 1000 more RPMs theoretically and put me in the right range. Engine is clean, runs smooth, it isnt the engine, that has been verified, just dont want to keep buying new props to find the right one. Anybody have a 20 footer with a 150 hung? if so what sized prop do you have?