I have a 20' 77 Rochell with a 460, cam, tunnel ram and 2 Holley 600s. Probably between 500 and 600 hp. I have a Jacuzzi Golden Eagle jet. Top speed on this boat (checked with gps) is 40-43 mph at 4500 rpm. Does this sound right? Am I maxed out with this set up? How can I get more speed? Is it possible?

Thank you,
Mike