Twill, the bitter truth MAY be that you are being limited by lack of horsepower rather than your prop. 16 rated HP isn't all that much for a 9800 lb vessel, and if your bttom is a bit foul or there are a couple of barnies on the prop... it just might not be enough.
And I don't think you have mentioned whether you can reach full rated RPM
with your current
setup... that bit of data would help us analyze your situation.
And for Cheech, I can't agree with you, nor can MIT and many other maritime experts.