you never said if that speed was from a GPS or the wishometer on the dash. Assuming you have a current model Honda 75 with 2.33:1 gear ratios then the numbers you gave says you are running -3.89% slip on your prop, so either your tach is wrong or your speedometer or both. With that said, the 17 3 blade will still be a better option than the 4 blade aluminum. The other thing to look at is motor position on the transom, you could raise it one hole to increase the RPM, but this might let the prop blow out to easy and you not be able to generate enough lift, or you could lower it one hole, this would lower the RPM slightly, but could give you more working trim and give you enough lift to carry the front and stop the porpoising. I used to have a stick steer crappie magnum with a 40 E-rude and I ran a 17 pitch stainless prop on it, I had the motor set one hole up from as low as it would go on the transom and it ran great at about 5600 RPM. I tried raising the motor one hole, and started blowing out the prop when I trimmed it all the way up and the boat had a tendency to porpoise. Back to the second hole it went and I was happy with it there.