[pbanders]

We have 87, 89, and 91 RON here in AZ. I ran 89 for about 6 months in my M3, and while I didn't really notice any performance difference (as judged by the unreliable "seat of your pants" dyno), the idle became rougher over time. I switched back to 91 and within a few tanks the idle was perfect again. My Box has only seen 91, and my 914 won't run on (knocks) if I use anything other than 91, and actually works best on 93 (I can slightly advance the timing and get a bit more power).