Well Whipsy, it makes no sense to go slow in your circumstance compared to what I get. You save a lot of time and get the same mileage then WOT makes sense. Some of us, like me are heavier loaded so don’t get that great a mileage. I actually base mine on litres per hour. I am also ballasted at my low speeds too so that makes a difference. I will have to do some extensive testing to discover the potential of my new Yamaha.
Gemini uses a 14X10 on his big Suzi and only gets 5800rpm @WOT yet I get 6200rpm with 14X11, Maybe I should try a 14X12. My best speed on one of my tests with an empty ballast and just me in the boat was 19mph, I think if I had trimmed the engine a bit I would have made 20mph. But I also had all my sails on plus all the stuff I carry around. I think if I strip the boat and try again I might make 22mph!