[sassage]

the Superhawk really does love emptying that gas tank, but it's entirely related to your right wrist...I've ranged from 30 mpg to 45 mpg depending on my attitude and riding style

[zerogara]

These twins are very heavy on engine breaking which wastes much energy if you are not careful. I'd like to bet that a slipper clutch will help mileage, for the rest of us clutching helps. I haven't ridden the F but the RC51 has a very fine line between acceleration and deceleration, and hates to cruise steady. Add to the fact of getting an endless rush everytime you open it up and hear it roar, only to slow own and do it over again and off in the atmospehre goes your precious gas.
Most people also mess with gearing as the stock on RC is meant for endurance racing not track or street at non-suicidal speeds.
This is a major advantage 4cyl bikes have, you can feather the throttle to where it is just cruising steady fairly easy minimizing fuel waste. Big twins seem to be unable to do this.