As someone who almost exclusively has ran the 10% ethanol fuel since the early 70's I truly can't say I've not experienced any problems as far as performance and mileage, and have really never saw any gain when I've changed to no ethanol for a test on anything from cars, motorcycles, chain saws, to lawnmowers. I do know, back in the day, the ethanol actually increased the octane rating of the fuels. running say 85 with 10% and then without , would definitely require me to reset the ignition timing or drive considerably more conservative. Also, altitude, ambient air temp, and humidity also would play a part in mileage as well as performance. I know that these things are the same today but the engine electronics and sensors are able to compensate for them today unlike the older vintage vehicles. The only problem with the ethanol I've encountered is in small engines that the fuel lines will deteriorate over about 3 to 4 years. Even then I wonder if the ethanol has separated out of the gas. My relative next door has this problem about yearly or sooner and I do about every 4 years or longer. We buy fuel at different stations so that is why I wonder about the initial mix. Last, pulling 13k with the 6.4, have ran from 87 (89 not available) and also 91 and truly can't see any difference in performance or mileage. I just stick with the 89.
