[THEFERMANATOR]

15 pitch IMO should be about right with a 4 blade. You're going to most likely lose some top end speed, gain some prop bite reducing slippage both of which will lower your WOT RPM's. With a 1.86:1 lower ratio, 5% prop slip at 5400 RPM's should put you right around 39-40 MPH for top end. A 17 at the same slip and speed would drop you back to 4750 which is near the bottom of your RPM band which would negate the 4 blade for better holeshot. Need to know your current performance numbers, RPM, speed, average load, current prop, diameter, pitch, and style to give you a semi accurate reccomendation though. And don't get hung up on pitch, some props bite REALLY good and will have no slip while others will have more. This isn't neccesarily bad, but you have to keep it in mind.