the higher the octane rating the slower the fuel burns. so what you want to do is run the LOWEST octane possible without detonation running to high of an octane for your combination can actually hinder performance. generally a street motor will never need more than 94 octane. now if your running on the ragged edge with high compression and boost , lots of bost , lots of spray, or very high compression(over 12:1) you need more octane to control the burn rate so you don't torch a piston. lots of other things play into this though like combustion chamber design, cylinder head cooling, piston shape, timing, fuel air mixture, and rod to stroke ratio. thats why a turbo buick at 30 psi needs c16 but an 13:1 big block with a new style head design and a conservative solid roller that makes the same power can survive on 94
HTH