Doesn't seem to mater what fuel I use, it all works. FWIW, I run "76 Brand" premium, works great. I took a trip to Mexico and used "PMEX Magna Sin" supposedly 90 octane, lead free. Ran into no problems.
My '06 seems similarly unaffected by octane and ethanol. It also seems confused about what it needs--the manual says "Super" (95 RON); the EPA compliance sticker on the frame says "91 AKI"; and a mostly-rubbed-away sticker on top of the fuel tank recommends mid-grade 89 octane. The bike in fact runs
the same, far as I can tell, on regular, mid and premium, with or without ethanol. It does sound
slightly different on 87 octane regular--no knocking or anything like it, just a slightly more "ragged" exhaust note. As a result, I default to mid-grade, followed by premium if available, regular as last resort. I don't worry about ethanol as long as it's 10 percent or less.
I downloaded a PDF of the 2005 manual from BMW's website (in theory, the two bikes are the same, especially since mine has an assembly date of 8/05). It gives more information, including AKI equivalents to RON numbers. And I quote:
The engine is designed for:
– Super unleaded gasoline (95 RON) (AKI 90)
It is preferable to use this fuel quality to comply with the nominal values for performance and fuel consumption.
In addition, the following fuel quality can also be used:
– Super Plus gasoline (98 RON) (AKI 93)
The minimum quality is:
– Regular unleaded gasoline (91 RON) (AKI 87)
It is recommended that gasoline with a fuel quality lower than (91 RON) (AKI 87) not be used