No surprises. The mid and big displacement bikes that have good efficiency are slow-turning, relatively short stroke, and EFI, tuned for torque, not horsepower. However, the big impediment to efficiency for motorcycles is wind resistance--motorcycles are about as aerodynamic as a broken brick. Aerodynamics is why a TW200 at 40mph returns about 100mpg, but the same bike at 60mph returns 60mpg. That is why a 250 engine in a dualsport motorcycle application can be tweeked to run about 100mph, and the same engine in a superkart will run 160mph. It pretty much takes 600cc to push a motorcycle to 160mph, and 1200+cc to push one to 200mph.