Octane doesnt equal MPG in any stretch of the imagination. On the turbo, your manual should tell you the difference between 87 and 93.
Oh, theres a difference in power. I had a turbo for a month as a loaner. Ironically, after reading something @WoodinvilleDan said in his super charger thread, i switched to 93 in my 3 and after 3 tanks there is a BIG difference in how it drives. The ECU in these cars is a much better learner than in the past and the 2.5l is an effing amazing motor.I was actually thinking the same thing as well. I have such an uncanny thirst for knowledge. I am still at 1/2 a tank of premium so I'll let it get abut a 1/4 of a tank, use low grade and see if there is much of a difference. i will definitely get back to the group this one.