Given the weight differential, initial cost, and operating costs, I would go with the single. If the boat already had twins on it, I wouldn't argue. However, with the new EFI Honda 90, I would be interested to see how the fuel consumption varied over RPM. I found the motor to be very efficient on a a 22 up to about 14 mph when loaded, but above about 4000-4200 rpm, fuel consumption went way up. I compare my 25 with a single 150 Yamaha to a friends 25 with twin carbureted 90 Hondas, and I plan on about 2.5 mpg while he plans 2.