http://www.mustangandfords.com/techarticles/30643/
Octane is the most important issue when it comes to selecting the proper gasoline. Octane is a numerical rating that indicates a fuel’s resistance to detonation. The higher the octane number, the more resistant it is to detonation. Higher octane allows an engine-builder to create higher cylinder pressures to make more power. If your engine does not detonate, rattle, or ping on 87-octane fuel, there is no advantage to using a higher-octane fuel.
Also, a common fallacy is that higher-octane gasoline burns faster or slower. As octane increases, the components that increase the octane chemically react in the combustion process to merely prevent detonation rather than change the burn rate.
-SF