[Fr. Frank]

Actual cruising speed for most boaters in exposed waters (not the Gulf of Mexico or the ocean) averages about 25-30 mph. I would compare the fuel economy of various motor tests at cruising rpm's and the speeds the provide.

I think Gillie's advice on the 115 Etec is very wise. You should be able to average over 5 miles per gallon at cruise. I think that will be more than 20% better than the 150, and 10% better than the 140 Zuke. You might sacrifice up to an equal percentage in top speed, however.

Denny reports the 115 Etec makes at least 8% over rated horsepower at the propshaft.
I have an acquaintance with an '06 21' Kenner VX who just bought a 2014 115 Etec to replace the original 135 hp Evinrude V6. He claims he actually has exactly the same top speed (41 mph), but went from 2.2 mpg at 28-30 mph, to "about" 5 mpg at the same speed, more than doubling his fuel economy.

He's a diehard Evinrude fan, and actually picked the 115 Etec over the 150 because it was only 405 lbs, while the 150 Etec was 435 lbs and $3K more expensive.