Originally Posted by cyrnel

Higher than recommended octane won't damage anything but your wallet. It might hurt performance, or help, but that depends on engine design and condition. If you've ever noticed knocking with 87 then real 89 or higher would help. If your engine has knock sensors and retards timing automatically then higher might help performance. It depends. I only have anecdotes with my old '90 GS. Check the manual for factory recommendation. Check out Acura forums for trends on stock engines.

For the disturbing part, mid-grade has often been tested as a profit item placebo, with similar or identical actual octane values to regular.

BTW, do a google for "gasoline faq". It's a long read but has great information.