The timing curve of your engine was optimized by the manufacturer for a given octane fuel. A higher octane fuel burns faster, upsetting that timing. If anyting, your car could run less efficiently on higher octane fuel.

The exception here are cars that have a high compression ratio to handle faster burns - but as I said, these cars will specifically require higher octane fuel. For instance, my Lincoln has a relatively high compression engine and my owner's manual recommends 91 octane fuel. My 87 BMW was orgininally optimized to run on 87 octane fuel, but when I added a performance chip that altered the fuel and timing curves of the engine control computer, I had to start using 91 octane to account for the difference.

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"If you hit them hard enough, anyone will put the ball on the ground." - Bronco Mendenhall