First off you really shouldn't make too many comparisons to auto/car set ups.
A marine engine is always under a huge load, kinda like a car constantly going up a 30% grade.
I would say that max rpm varies a bit depending on the boat that the motor is in. If you have a 19 ft boat, I would say 5000 rpm max. If you have a 24 ft boat, I would say 4800 rpm.
In any boat, you prop it so that under perfect conditions it will pull up to max rpm. If you prop it too small, then you will always be on the limited which is bad. It is a trial and error kinda thing as is also dependant on what you use the boat for.