Octane is a measure of a fuel's resistance to pre-ignition (ping).
In California, you see R+M/2 on the pump. Research+Motor/2. Research is the theoretical point of detonation a fuel can take, and Motor is the number they got from their real tests. Incedentally, they use a two cylinder engine that they can change the compression ratio by screwing in or out the roof of the pistons!
While a higher octane fuel will resist pre-ignition, it also is more difficult for your ignition to fire it off. This is why some vehicles seem to "slow down with higher octane fuel".
Running higher octane fuel will do nothing for performance if your car runs fine on the cheaper stuff.
Many people confuse higher octane as meaning a more powerful fuel. Not so at all.
There is also merit to the idea of fuel being different from manufacturer to manufacturer. My '71 and my wife's new car both get better mileage from using Union 76 fuel.
TIGER EFI - Electronic Fuel Injection for the Traditional Pontiac Engine.
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462 cid/ 6x-4/ TH400/ 3.36:1/ 28x10.5/ 3880#/ 12.35 @ 109.36/ 1.69 60 ft/ 4 wheel disc brakes/ 15 mpg