Red, until you pick up WB's simulator, I thought you may be interested in a few numbers ..

No wind, no AC, sea level, summer petrol.

miles per hour .. mpg
61 ... 60.78
64 ... 58.11
68 ... 54.75
71 ... 52.36
76 ... 48.65

My nmeumonic that I remember is that the Prius is part of the 60/60 club

Oops, I just saw that I had the Cd at 0.25 rather than 0.26. The mpg's are off by one mpg or so .. Sorry