When gas was less expensive I used 93, In my 330ci I have used only 87 and car runs the same as if I used 89 or 93 yeah I kno it's not recommend but when gas is almost 5$ for premium yeah forget about that. On the other hand I only use 93 in my boosted ZHP, and also used 93 in my M3. To me it's just a preference or if you could afford it.
Instagram : Krystian_E46
Owner of many E46's :)
[Currently own 2004 M3, 2004 ZHP HARD MOTORSPORT Flares & Centerlocks, 2005 AA 2.5 Kit ZHP(SOLD
), S54 Sedan, 01 330ci and 1 Coupe 1 Sedan 1 E46 M3 parts cars]