Unfortunately, most people insert too many variables into their routine to determine beyond a doubt, that one brand of gas provides better mileage than another.
One recent trip that I took would be good test. Leave home, drive 300 miles to destination.
Then fill up, and drive home. The same route, the same day, the same speed, in the same car.
And this even inserts variables as I filled up at a different gas pump in Ohio. The gas nozzle could have shut off earlier or later than the gas nozzle that I filled up with in Illinois... there could have been more or less wind in the morning, than in the evening... there was still some gas in the tank from the other gas station when I refilled in Ohio...
But, whatever makes you feel warm and fuzzy... I'm all for it!