Sorry to disappear from the forums! It's good to be back! I've been running non-top tier fuels since there is nothing near my new home, but last night I ran a top tier (Phillips 66) since I was near a big city. I think there was *some difference*. I got right at 35 and that was with A/C doing 65. Typically I get 33 or so. I wouldn't take this as a scientific study, but maybe someone could try?