Well, I have recently transitioned from a diesel inboard to a Yamaha 300HP outboard. MY experience with the inboard is that you should always strive to get the manufacturers WOT RPM. Hence your prop configuration should be such that once your boat is loaded with everything you intend to have on board then check your RPM at WOT. If it is not within a reasonable range of the manufacturers specs then you need to change your prop to accomplish it or change your on board load. Granted a clean bottom also makes a difference. Overloading or underloading the engine, at least on an inboard, is not good for the engine.