I can attempt to help you with the 2765. I get about 1.25 to 1.5 mpg at a comfortable 3500 rpm. Anything less than 3000rpm, I drop off plane, and greater than 3500 just wastes gas. My only regrets with this boat is fuel capacity which is 78 gal. Figuring 10% unusable, that leaves only 70 gal; meaning roughly 80 miles tops. AND, that's with perfect conditions.
Everything else regarding the boat, I love. Have added: Bennett ATC, Raymarine Autopilot, Navman GPS w/ fuel monitors, Lewmar windlass, Centriod fuel sender, and several others I can't remember right now.
Ask any questions, and I'll help.