fish-addict,
It doesn't have anything to do with horserpower ratings. It has to do with the physics of the jets vs. the props.
I think if you talk to anyone who has an outboard with a prop and jet attachment, the prop will show the rule of thumb 30% more efficient numbers in speed and fuel efficiency.
I have a jet but I don't kid myself that it is anywhere near as efficient as prop.
Advantage for jet is shallow water operation, not speed or fuel efficiency.
Brion