That RPM and MPH works out to approx. 42 MPH with an 18 pitch prop, so that probably what you have since you see the number 18 stamped on your prop. I also see the 21, but don't think you have a 21 pitch prop because that would give you about 50 MPH. This is assuming your drive is a 1.98.
So your current prop size is probably going to be good for water sports and hole shots. If you're not really interested in water sports and just like cruising around, you should try and 21 pitch prop. It will bring your WOT closer to specs and give you higher top end.
I personally like aluminum because the blades flex, and, there is less shock transmitted to the outdrive if you hit something hard with your prop.
2006 Bayliner BR205
A1 Gen 2 1.47
5.0 carb engine