Although I don't believe this for a minute ... I'm gonna give it a try. My wife drives the car primarily, She averages a rock solid 33.5 MPG per tankful on her commute. I put 89 in the car today, and am not going to tell her. We'll see if it makes any difference in MPG over the next 3 or 4 tanks. After 3 or 4 tanks of 89 ... I'll try some 93 for the same amount of time.
We shall see .... :D Although I don't believe there will be any difference ... I truly hope that there is.