Relative merits of propellers

[Flatswing]

I would suggest 2 things:
1) Consult the owners manual for recommended WOT rpm for your engine
2) buy a photo tach (<$25 at Amazon or harbor freight) comes with little sticky reflective patches - put 1 (only) on the side of your flywheel (& make sure there are no other reflective tapes on it too)
Your starting point should be what actual rpm do you achieve with a clean bottom & underwater gear at WOT. Ideal is to to be able to hit the number recommended for your engine. Some sailors & trawler owners deliberately over prop to lower the rpm by approx. 300 rpm claiming quieter cruising, possibly improved fuel economy but There is a good reason the engine manufacturer recommends a specific WOT rpm!
Your cruising speed will be whatever that engine & prop combo delivers at a comfortable rpm. You will probably find this “by ear” but by all means confirm with the photo tach & compare to the duty rating for your engine.

[Mike Banks]

The advantage of a two bladed prop is fitting it so that it lies behind the keel out of the water stream when it is not in use. This requires a mark on the coupling so that the shaft can be turned by hand when the gearbox is in neutral. It stops that damned annoying prop spinning and creates less drag.

Whether or not it is ideal for your vessel is another matter--but for small vessels a two bladed prop works fine.