I have a 1972 Newman 15' Tri-Haul. It has a very strong running 1974, 85 HP Evinrude V4. At WOT the Tach is pegged above 6000, and I am getting 40 MPH at WOT, when I back it off to around 4800 I am getting 30 MPH. This boat has an unbelievable hole shot and will turn on a dime with no list and not loose any RPMS doing it. The prop is a 13 1/4 X 17, I need to loose 600 to 800 RPMs to get to in the 5500 range. What Pitch should I be running.