Higher octane isn't to make more power... in fact in a car designed for lower octane fuel, higher octane will actually decrease performance.

The higher the octane of a fuel, the more it can be compressed before it will self ignite.

The L67 motor in the supercharged GP is designed for higher octane fuel. It's compression is fairly high, and with the supercharger, it's very high. If you use lower octane fuel, that fuel will ignite in the cylinder before the spark plug fires. This causes knock. The PCM will attempt to adjust timing, but with very low octane fuel, it can't eliminate this knock caused by the fuel igniting early.

That knock is actually the fuel igniting while the piston is still moving upwards, trying to compress the mixture. This creates tremendous stresses on the piston, and can blast a hole right thru the piston itself.

It MIGHT be safe to run lower octane fuel if you were to remove the supercharger belt, as the compression without the supercharger will be much lower.

But assuming 20 cents extra for the good stuff, you are only talking $3.00 extra per fillup. Is it worth the trouble to use the lower octane fuel? You can easily save more by just driving a little slower, not punching it off the line, etc.