Hotsauce -- you and I were thinking the same thing...

I've actually run my VX (stock engine) through a test of 10 tankfuls of 87 and 10 tankfuls of 93. I do about 50% city driving and 50% highway (with offroading another 10% -- wait a minute...) and I found that my gas mileage did go up slightly with the higher octane (something along the order of about .5 mpg).

My main goal in the test was to see if the higher octane was actually cheaper to run (to see if the better gas mileage would compensate for the higher price at the pump) and I found it really didn't.

If I remember correctly when I did the test it worked out to about $.08 per mile on the 87 and about $.10 per mile on the 93.

In terms of performance, I honestly haven't seen any performance dip or higher knock count on the 87.