The reason why I ask is that in my new jk I used regular for a few tanks with no problems but the last time I filled up with regular I got pinging, so I added premium when it was a quarter tank down and it went away. In my element, since I moved from idaho to washington the honda sounds like a bus when im going up hill and accelerating. Im thinking that the gas is formulated different here than it was in idaho. That or just he elevation differance is changing the way my cars run. what that has to do with the 10% ethanol is I figured I'd just start using mid grade and I could justify that in my head if it had less ethanol. I think I just found my answer on about.com, here it is
REFORMULATED GASOLINE
"In some major cities with air pollution problems, reformulated gasoline is required. It is an oxygenated fuel, that burns really clean but can slightly lower fuel economy and engine performance. If your engine is really dirty with carbon deposits, it will also cause pinging or premature burn. In these types of situations, you may want to consider stepping up to the next grade of gasoline.
The bottom line is to use the type of gasoline recommended for your engine. In some cases, like towing, or other stresses on the engine, you may find a higher octane fuel helpful."