I would focus on what the manufacturer's recommended Max. RPM Range for the motor at full throttle. Then see where you're actually running at, at Wide Open Throttle (WOT).
Manufacturer Max. RPM > Actual WOT RPM = Overpropped
Manufacturer Max. RPM < Actual WOT RPM = Underpropped
This is, of course, assuming that there are not other variables affecting performance, such as :
dirty hull/growth on bottom
engine is running clean (timing, compression, carb., etc)
boat isn't overweighted
These are just general rules of thumb to go by. Are you having specific problems?