I'm running 21M now and will switch back to the 23M. The 21M turns 6600@56 MPH. When I ran the 23M it turned 5400@51 MPH. I have not ran the 23M since Yamaha replaced the powerhead. I have not ran a 4-blade yet but plan to this summer. If you are moving a 2420 more than 52MPH with a load be glad. I believe no matter what you do with props you will not gain that much more than you are running now and will lose the extra speed just as soon a your prop gets dinged. Nice Boat.