If your going for fine tuning you want to prop it with the load you would usually be carrying, and for pitching a prop you want the water flat so you can hang on to wide open throttle without coming out of the water.
When we prop boats at work we test the full range from light load to fully loaded up in 100kg increments. Then you can look and see what pitch suits, one that wont over rev when light and works the best loaded, it can take a long time and alot of propellers!. Once you have pitched it right you can then look at how many blades, what type of prop etc. We have got pretty good at it these days and will usually guess it within one pitch and prop type!. We always have a bet on to see who gets it right. Usually the boss annoyingly!