I've heard at 55 mph some owners (no AC) are getting in the low thirties.
Which just shows what really can be accomplished when the car companies are really trying. Imagine telling a Corvette engineer in 1970 that a 2009 Corvette would pull high twenties low thirties in fuel mileage, 0 to 60 mph in only 3.6 seconds, hit 100 in 7.9 seconds, and 150 in 17.5 seconds and still be able to hit 200 mph.