I've been over this time and time again, pitch and diameter are a starting point, blade composition is not that important till you get above 60 mph. Design and profile are the most important thing about props. I can take 10 different 19 pitch props and all ten will perform differently. Blade surface, rake, number of blades, blade design, ventilation holes, over hub or thru hub, cup, tip roll, etc.......They all make a difference. In lower speed props, generally the aluminum wheels are more of a generic design and perform good all around, lower end stainless props duplicate the performance of their aluminum counterparts. Every put a stainless prop on a Volvo single prop out-drive? It will run slower than the aluminum one. When you get into higher end props, they generally have more specific design goals(higher prices too).Don't always go just on the pitch either, there are several prop manufactures that rate their pitch differently. Mach was real bad about this(they are out of business now), their 20 pitch four blade checked out at 24 pitch on the blocks. I've had some props that none of the blades were even close to the same pitch(Eagle and Turbo). I've sent props to have them lab finished(by Merc racing) and the boat slowed down afterwards. Point being, they are very loose guidelines, until you bolt it on the shaft, you will not know for sure. Aussie, from my experience with the 3.7, you'll be hard pressed to find a better wheel for what you are doing than a Mercury Mirage plus. you need to base line the engine with a known unaltered prop to get a feel for where you need to be, but from there own, its trial and error. BTW, its hard to beat mercury props.

I did answer your question in my first reply Aussie.
And read what SpareParts just said about props. His reply is basically a longer and more detailed version of what i said when I said:

The best way of learning more is to read and listen but not speak that's why I am asking a lot of questions