[spareparts]

that six runs much better proped at 4000 to 4400 rpm

GMC. my point was that without rpm information, horsepower ratings can be missleading
A couple of years ago, Mercruiser introduced the 5.0 MPI rated at 260 Hp at the prop, they were claiming it would do the same as a 5.7 carb, what they neglected to point out was the 5.0 needed to turn 4800 to 5200 rpm to make power( it had a peaky hp curve), while the 5.7 only had to turn 4400 to 4800 to make the same power. the 5.0 would run faster than the 5.7 in a light boat( checked it myself), but put the two in a medium to heavy boat, the 5.7 walked all over the 5.0, it wasn't even close, with out the torque curve referenced to rpm, most people wouold assume the 5.0 would do the same job(thats what they were telling the salesmen, who were telling the same to the customers).