wrote ...

Based on past discussion, I am under the impression that an outboard
will work the most efficient if it is being run in wide-open-throttle.
This means I am looking for a motor that can satisfy the requirements
stated above when it is being run in wide-open-throttle (instead of
getting a BIG motor and then running it at low speed).

You may want to rethink running wide open at cruising speed. Reliability will
suffer and fuel consumption wont be significantly better than a moderate sized
motor running at 70-80% of full throttle.

-rick-