Like others have already said, there is something to be said for not running something mechanical like a boat engine at capacity. De-rated motors whether intentionally that way by manufacturer limitation or by operator choices has shown to reflect longer life span on engines and healthier ones at that. Personally, I will gladly take a bigger engine that does not need to run at maximum capacity routinely to accomplish the amount of work I am demanding from it. 6.0 V-8 in my tow rig, I get 12-15 miles per gallon towing my boat but I am never over revving the engine to get the ensemble moving or keep it moving, even going up hill. I can buy a ton of gas for the cost of a drivetrain repair or even worse replacement which was the driving force behind getting a dedicated tow rig to haul our boat around instead of using my wife's daily driver.
'86 Comp TS6M
Riding Connelly Skis and Hyperlite Boards
Rarely ballasted with up to 1500 pounds of ballast