Originally Posted by JohnnyMW
........ I've heard a lower pitch will give better fuel economy too!!
Could go either way, propping is a black art & there are no hard & fast rules. That's why you need to experiment. If the engine can spin it, the higher pitch will give you more top speed, but lower "holeshot" (acceleration) & vice-versa for the smaller prop. If you cruised all day at a constant-ish speed, the taller prop could in theory
give better economy, but would use more fuel accelerating, so like I said, trial & error.
If you're going out lightly loaded for a jolly on a calm day, stick the bigger prop on. Fully loaded, rough seas, towing toys, skiing etc. then the smaller prop will probably be the better option IF you can achieve WOT (Wide Open Throttle) RPM i.e. full beans, pedal to the metal etc.