I had to put half a tank of 89 in my M once. 3 am, back country roads, I was lucky to get anything.
Felt horrible doing it...
However, my dad puts 87 in his 2012 528. NEVER uses mid-grade or premium. It's shameful really...
"When makin' a questionable decision, sometimes the only way to find the answer is to shut your eyes & mash the pedal to the metal, you guys."