Maybe I should have stated my sources - the American Petroleum Institute themselves. Here are direct quotes from their website:

http://www.api.org/aboutoilgas/gasol...ine-octane.cfm

"Octane number is a measurement of fuel’s resistance to engine knock. Engine knock is an abnormal combustion associated with using gasoline with too low of an octane number. Ordinarily, your vehicle will not benefit from using a higher octane than is recommended in the owner’s manual."

"Knock Sensors
Many modern vehicles are equipped with an electronic device that detects and eliminates light knocking before you can hear it. The devices suppress knock by retarding the spark."

"Gasoline with a higher heating value (energy content) provides better fuel economy. Traditionally, premium gasoline has had a slightly higher heating value than regular, and, thus, provides slightly better fuel economy, but it is difficult to detect in normal driving. There can be even larger differences in heating value between batches of gasoline from the same refinery, between summer and winter volatility classes, or between brands of gasoline from different refineries because of compositional differences. The differences are small and there is no practical way for the consumer to identify gasoline with a higher-than-average heating value."

But this is from the API, so they do have to claim that there is some value in that premium gasoline you are buying. They do represent the petroleum industry, you know.

And higher compression engines don't actually gain any power using higher octane gasoline, they just don't lose that portion of power that sometimes happens during acceleration from pre-ignition (knocking) that they would with lower octane. The power in the gasoline is the same, it's just the point in the compression cycle when the ignition happens that determines how much power the engine gets out of the gasoline. Knocking happens when the fuel starts to ignite before the piston reaches the top of its stroke. If that happens you lose horsepower because then some of the energy from fuel combustion is working against the power stroke of the engine. That's being a bit simplistic because the ignition phase of the stroke actually does start just before the absolute top of the stroke (Top Dead Center), usually about 10-25 degrees before TDC, but the maximum power of the combustion cycle doesn't happen until just after TDC. Knocking happens when the fuel burns too fast and the maximum power of the combustion happens before TDC instead of after. Modern engines will detect that this is happening and retard the spark so that maximum power happens after TDC.