I still can't understand the reticence about water cooled engines. For a start it would remove a huge number of problems such as cylinder cracking due to shock cooling. How many engines a year are killed by that little issue?
With the levels of maintenance that is carried out on your average GA machine, how much of a problem would it be to keep a water system operational?
With regard to the fuel consumption of a superbike, when on a track and caning the life out of it, you will struggle to see 30 MPG, but then again you are using full throttle for much of a lap with lots of accelerating and braking thrown in again using massive amounts of fuel. (some might say unnecessarily!) Take the same bike on to the motorway and cruise at 70-90 mph and I personally get nearer to 55-60 mpg with no problems. Whilst a bike may not be very heavy, they are not exactly aerodynamic, especially with a lump like me on the back!
Bike engines are amongst the most efficient petrol engines on sale today, but again they are designed for a totally different use than a horrible great Lycoming. You put a lot less fuel in and go almost, if not faster than most light a/c!! Not very good at aero's though!