I think the Volvo's are excellent drives, I have one on a 21ft Cobalt with 5.7GSI 280hp. I know the same drive is used behind the new 496 with 425hp. I like quick hole shot regardless of the amount of people in the boat it is still a lot better with the two props.. Top end on my boat is somewhere around 60mph I have seen 63mph on the speedo. I think that speaks volumes about the drives efficiency coupled to a boat that isn't known for SPEED. The horsepower the drive will take is a good question. I'm thinking you would be
pushing it above 550hp. They are supposed to be extremely strong but how strong I don't know.