So far, there are indications that there is indeed some improvement to my fuel economy.
Normally, when the fuel gauge gets down to the halfway mark, is I have gone 250 miles, it's probably going to be a pretty good mileage number when I get to the refueling point.
Yesterday, the fuel gauge got to the midpoint, and when I checked I had driven 262 miles, about 4.8% farther! Of course, there are all sorts of variables at work here: was the needle really in the middle of the tank? Was it moments before adjusting down again? Was it because I drafted behind a tractor trailer on my way home two days ago?
Clearly, the experiment must go on for more than one tank. I have behaved somewhat erratically so far on this first experimental tank of gas, as truly I did draft behind a tractor trailer going home on Wednesday- but I was going much faster than I would have ordinarily driven (~70-75 miles per hour) in order to maintain the draft. And yesterday on my way home, I did several jackrabbit starts to try to beat other cars to the next intersection (hey, I felt that I was in a hurry and thus more important than everyone else!).
So, overall, my driving habits so far for this tank aren't really representative of my overall driving style. Well, that may be a lie. I frequently have one or two spasms each tank where I floor it for no good reason.
But the experiment will proceed. I am curious to discover if this "4.8%" increased distance on half a tank will equate to a "4.8%" increase in overall fuel economy. I don't think there's a correlation that strong, but if there is, my mileage may be pushing 40 mpg on a regular basis, rather than the normal 37.5-38 mpg.
Time will tell.