OK, most people have said it as it is: use of more octane than minimum required is a waste of money.
And please note something: MORE OCTANE GAS DOES NOT PERFORM BETTER.
The octane level describes a protection ratio for compression and spark advance, (engines that have higher output) and thus they need higher octane. This does not mean that a higher octane gives higher power. This is just commercial. If it was that easy, you could use 120 octane in your engine and get more power. They would have invented 200 octane gasoline. Be serious.
There is ONLY ONE car thaat performs better with higher octane: the SAAB 9-3 and its adaptative spark cartography, that advances the spark always to the detonation limits. Use of higher octane fuel will accept more spark advance.
I have a BMW M3
with four easily choosable cartographies: for 95 (european super unleaded), 98 (european extra unleaded), 97 (old european super leaded) and... 91 (american premium). I have been running her for the last eight years on 98-cartography using 95 and nothing happened. She has 175.000 kms and works like a swiss clock.
One day, I tried the 91 cartography and the power above 3.000 rpm was exactly the same, and acceleration times too. The only difference was a weak torque below 2.500 rpm and an absolute lack of it below 1.500. But HEY!!!... this was not because of the gasoline (I cannot find american gas where I live, it was actually burning 98 when I tried it), it was because of the cartography.
So, if your car does not have a self-adaptative cartography, or one you can program, whatever kind of difference you may feel is entirely SUBJECTIVE / PSYCHOLOGIC.