I've always had the 16 too. I get about 42 mpg. Most of my riding is half freeway at 80-85 indicated, and half city streets.
I find that my mileage greatly improves riding the twisties, keeping the engine in the 5,000-7,000 rpm range up to 55mpg, so I'm thinking it's more a factor of (lack of) aerodynamics.
