I've owned Mercurys, Evinrudes, and Johnsons. All were great dependable motors. I'm currently running a 150 Johnson on my bass boat, and a 15 Evinrude on my Jon boat. I wouldn't hesitate to buy a Yamaha if I needed a motor and the price was right. From what I've seen and experienced, one is about as good as the other. Fuel consumption? At full throttle, my 150 burns about 15 gal per hour. I'm sure some four strokes do a lot better than that, but the difference isn't worth my trading. I usually run about 4k rpms when going long distances. It cuts fuel consumption in half. I bet you'll find that you can reduce your rpms to about 4000-4500 and do the same on the barge and only lose <5 mph. That's assuming your barge is propped correctly.
Savage
Savage