Folks on the high performance board have reported seeing a 2-3MPG difference when travelling from CA to another state and back, when burning the other state's gasoline.

Botique fuels are another bane in my life, IMO we'd be better off with a single nationwide standard even if it were the cleanest possible blend. If there were just one supply issues would not be as bad and the manufacturers could better tune the vehicles since they would know there was only one fuel to deal with. The only differences should be 87, 89 and 93 octane for lower elevations and 84, 86 and 89 for higher elevations