Originally Posted by Ridley

High octane gas will actually reduce the power. The lowest octane gas you can run that doesn't pre-detonate will yield the most power. To need high octane gas you must have a high enough compression to cause normal gas to pre-detonate. Octane in itself doesn't increase power, only changes the requirements for that fuel to burn completely.

Some fuels, like quite a few of the VP lineup are oxygenated fuels, which is a whole different discussion. Many of which will yield good gains, and there's generally good information on the website about what their fuels were designed for and the engine parameters needed.