There is a gentleman who has a 23 Offshore with a 1988 454 330hp. He clocks 63mph on GPS with full 50 gallon fuel tank. The Mercruiser 330 was crank rated and made about 295hp at the prop running a Quadrajet.
330hp = 63mph spinning a 24p 3 blade turning 4800 RPM
330hp = 66mph
500hp = 83mph
525hp = 77mph spinning a Mirage 25p 3 blade turning 4900 RPM
680hp = 91mph (best of 92.6 fastest in the US) spinning a Spinelli 28p 4 blade, (exact model unknown) turning 5750 RPM
*all of these speeds are in freshwater
1972 16 OB - C16B-63 - "Surface Tension" Resto Project
1974 16 OB - DMR16106017-B - "The Mule"