It won't matter in
your car. Money out the tailpipe.
A car needs to have a knock sensor (or a driver manually adjusting the timing) to gain a theoretical benefit from higher octane (the computer will advance the timing to take advantage of the fuel, so torque will be increased).
But the higher octane only increases
peak torque ability, so it probably won't make any difference to the average driver tooling around at part load.
Then again, if you exclusively Pulse and Glide (moderate to high load accel) an engine with a knock sensor & premium fuel, it may help.
Here's some good info about octane & fuel economy:
http://fuelsaving.info/fuels.htm