If your current prop’s performance is acceptable (WOT is within manufacturer’s guidelines) -- Choose a replacement prop that is very similar to the diameter and pitch of your current boat prop. You might consider upgrading to a different material such as stainless steel or trying a 4-blade prop instead of a 3 blade.
If your current prop is unsatisfactory — What if your engine operates at the wrong rpm at WOT? Pitch and rpm have an inverse relationship. Increasing pitch reduces rpm and reducing pitch increases rpm. A 1" change in pitch will usually result in a 200 RPM change in engine speed. Therefore, if your engine operates below the optimum proper rpm, you should consider a boat propeller with less pitch. If your engine over-revs, consider increasing the pitch. Example: Your sterndrive tach limit (red line or rpm limit) is 4800. Your motor at WOT with full trim only turns 4300 rpm. Buy a prop with 2 less pitch to bring it up within 100 rpm ofyour tach limit. Your acceleration will improve and your top end will stay the same or improve because your engine puts out more power closer to its rev limit.
You might also consider changing the propeller size to affect a specific performance attribute. A lower-pitch power prop makes it easier to pop skiers out of the water. Tournament bass boats may need more top end speed and should use a boat prop with a higher pitch. Houseboats and cruisers care more about efficiency at displacement speeds, therefore they require a lower pitch to achieve low-end power and the largest diameter their lower unit can handle.