Class A vs class C

8 to 10 for a gasser, a little more for a diesel. However, since diesel costs more, you get about the same mileage per dollar.

I once ran a test. I get 8 mpg at 62 mph. I once did a 2,000+ mile vacation driving 72 mph and got 6 mpg. That is a 25% drop in mileage for a 15% increase in speed. Not worth it.