I rarely see more than a couple tenths variance at the most and that's the truth no matter who wants to believe it. That is why the 1+mpg difference was so surprising to me. Some people may have a hard time believing that and I just don't know what else to say about it.

 

I used to get rock solid mileage that only varied two to three tenths. however, varying degrees of traffic congestion screw that up for me.

 

I leave the house early and leave work early(relative to traffic) so it's pretty much 75-80+mph for a total of 100 miles everyday for work. Then if I go anywhere in the evening but, that mileage doesn't add up to too much just messing around here and there. If I didn't go through a tank of gas so quickly do to work I'm sure the stop and go/short trips out would play a bigger role in mileage differences but, right now they don't seem to.