FWIW: I've been using regular 87 octane gas in my 2004 BMW 530i (e60) for over 10 years now and it has 214,000 miles and runs perfectly, and has more than sufficient power. When I first owned the car, I used 93 premium in it , but then experimented a bit, and now for almost 10 years have been running only 87 and, again, absolutely fine. I have been driving primarily in Pennsylvania and NJ with mixed highway, suburban and a little urban driving.
I don't see the benefit in this case to run premium for maybe a tiny improvement in power and fuel economy. The economic equation has tilted more severely toward the use of lower octane a couple years ago when the spread between 87 and 93 rose from ~20 cents to ~60 cents per gallon.