Next on the list of factors is pressure. When you increase the surrounding pressure, you can usually dissolve more gases in the liquid. Think about your soda can. It is able to keep the fizz inside, because the contents of the can are under higher pressure.
Assuming a prop, it depends on how you are propped but with a redline of 6000 rpm, most outboards perform best with a cruise in the 4000-4400 rpm range. If you want top fuel economy, get a floscan or such and see what is the most efficient for your engine and prop.
A sterndrive or inboard/outboard drive (I/O) is a form of marine propulsion which combines inboard power with outboard drive.he drive unit (outdrive) carries power from the inboard engine, typically mounted above the waterline, outboard through the transom and downward to the propeller below the waterline.