I use to be a service advisor at a BMW dealer and I can say that most BMW owners are the biggest cheap asses out there and will bitch about maintenance till they get it for free or a price brake. If the car calls for 91 or better then that's what I would use.

 

I know I felt cheap when the anti-freeze for my car was $29/gal.

 

Back on topic (for off-topic...)
https://cbrforum.com/m_525404/tm.htm