Originally Posted by Andy
Higher octane fuel isn't a "better" or more powerful blend of gas, but rathrer one that's more resistant to knock, or detonation. If a motor is built for and runs fine on 87, there's not benefit to running anything higher in it. However, if your motor has higher compression, lots of timing or forced induction, the extra knock resistance of higher octane fuels becomes nessicary. All DOHC VTEC engine's require 91 or greater and have a knock sensor that will listen for detonation and pull back the timing to protect the engine but it won't make as much power. Long story short, yes, you need premium fuel.
Agree'd, with that said run 91 octane, no need for anything higher unless your running forced induction or have raised your compression.
You always want to run the lowest octane that you can get away with. Running higher octane will not increase power and may ultimatly effect fuel economy and it will effect your wallet in a negative way.