I have always used to run my car on 91oct. Until a year ago.
I started to take my car to an small indy shop that run by a Bmw veteran ( 35 yrs in service ).
While he was changing the engine oil I asked him about the octane rating and possible impact of using lower rated ( 87oct ) fuel. He said, there is no harm of using lower oct fuel especially on the Hwy. but he recommended mid to high in the city. Either way there is no harm to the engine. With lower octane there will be small ticking noise coming out of the engine ( not lifter ticking ). Since I drive mostly hwy I have switched to lower oct fuel. No issues at all.
I can not speak for turbo engines regarding that. But my experience with lower octane fuel on N52 has been good. In a situation like Sandy, i could careless what bmw says as long as the car is running.
At the end its is just A car. Hope everybody makes it out ok from Sandy.