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.
For instance, an outboard motor tune up costs around $300 to $400 depending on the level of service required. The average cost of an outboard tune up is around $300 to $400, depending on the level of service the mechanic does. Meanwhile, an outboard motor rebuild runs around $1,200 to $4,000.