Mine is not stock, so that can change a lot, but I have been testing mine....I drive about 25-30 miles of my 40 miles commute on roads that have a speed limit of 55-65. Everyone (myself included) Usually runs at LEAST 75, and I never worry about being too hard on the stupid pedal. SO, with fuel prices being what they are I forced myself to drive no faster than 55 and to accellerate like normal traffic (slower than I could normally stand) I haven't officially finished this tank, but by looking at the gauge it looks like I might have gained 1mpg at best, this means nothing because every once in awhile I get a little better mileage for some reason. (Maybe I top off the tank a little more or something) Good luck on your quest, but I can't seem to significantly change my mileage no matter how I drive it. I have heard that 1800rpm is the "sweet spot" for cruising speed. If it's true, that explains my problems. With my tires I have to be doing 75 or so to get that, at 55 I am under 1500rpm.
-Aaron