Generally, I too have seen the same mileage figures from different brands but as I have had BP card since 2005, that's what I use (unless out west, then it's Shell as there ain't a lot of BP stations). If the motor is set up (timing, compression, etc) to use 87, using 91 or 93 will not do anything but drain a wallet faster.

There have been a few tanks over the years where I really got some bad gas that ran crappy and got lousy mileage ....
.... and once in a police car which always filled at the office tank on midnight, it was the night after they had moved the pump from near the back door out to a shed on the edge of the lot, guess they finished late and then I come along on late shift needing a fill up. Pipe dope completely blocked my inlet sock and filter. They ended up putting a new pump and filter and etc on the car as well as completely flushing the tank.

In all our travels when I was a kid, when we lived in Del Rio and traveled to Va. or after we moved and went back for summer visits, my dad would never get gasoline anywhere in Louisiana ....