I did a masive report on this for an online automotive website about 4 years ago. Basically the short and skinny is this. Higher octane does not mean more power. In fact it can mean the opposite if your car is not set up for it.
The lower the octane, the bigger the burn. Lower octane fuel combusts much easier then higher octane. Octane is the label that describes a fuels resistance to ignite. Like a diesel, high-compression vehicles need higher octane because as cylinder pressure increases, the fuel will try to ignite. (Diesel engines have no spark plugs due to the massive ammount of compression. The fuel ignites itself).
So, in real-world terms this means that anything over say, 93 octane on a stock (no internal mods/blower/turbo/nitrous/mega-advanced timming) is actually going to give you a net loss in power and economy. People have a hard time wrapping theor minds around this sometimes because the oil companies have done so well marketing the higher octane fuel as a magical power increaser. It is just the opposite.
What I am trying to say is that you should save yourself a $1 or so a gallon and just stick with the standard premium unless you are modded as stated above. I am sure there are going to be people here that are going to disagree with me, but you can research it yourself and see that I speak the truth.