Lucky you can get gas without Ethanol. Not available here.
Only Sunoco has 91 by me, so I typically fill up with 93, preferably Shell.
Putting under 91 just does not make any sense. If you can't afford premium gas, you probably should not have purchased a BMW.
2017 540i xDrive Dark Graphite/Mocha Nappa/M Sport/Driver Assistance/Driver Assistance Plus/Cold Weather/Multi-contour Seats/Premium/Gesture Control/Soft-close doors