I'm exaggerating about the 91 octane being crap, and it generally is considered a premium grade here. But if I had a preference, I wish I had easy access to 93 or higher. PresaMats car makes a more power than another one of Shiv's customer who's car is located in California and that car has an exhuast! Presa's car is the strongest car I've read about so far.
http://www.e90post.com/forums/showthread.php?t=36987[
There are variables between cars, but part of the increased power output, both stock and modified can be attributed in part to the increased octane rating. I've seen dyno charts of some vehicles running 87 vs 91, the difference was up to 10hp. Properly tuning a car to run higher octane, such as 100, can net you 20-30hp over 91.