I get a steady 50 mpg at 49 mph in 5th... I can never drive at that speed for very long, though.
I usually drive 60-70 mph on the way to work and back. I actually get better mileage when driving 65-70 because I draft more (traffic is pretty tight). If I drive more slowly, everyone just passes me by. I average 33 mpg on my commute, and only 34 mpg when driving on the interstate at a steady 65 mpg. Go figure. Forced P & G?