I moved from Istanbul, Turkey which is in european continent. We have unleaded 95, 98 and even 100 octane(shell vpower) options in Turkey.

I had an .Opel, Astra egelance 2003 automatic transmission 1.6lt(bought it new). I used to use 95 octane which is the regular option. And after all the adds about highest octane, i decided to put 98 octane(when it was 2 years old). Violaaa!!! Its like i bought a new car again.

I noticed couple of things with the car.

1) Car got faster on jackrabbit starts which you need it alot in Istanbul.

2) Car made less noise over the speed of 100mph. Once i put 100 octane and could get to 125mph with less noise. I miss those days.I will be in jail in states for that speed.

anyway,
I havent tried using anything else other than regular in my 4runner. Im quite happy with the way it runs and handles and wont need more. But im sure it will make so much difference if you put higher octane in it.

If you use higher octane for a long time, dont switch back to regular, you might be dissapointed with the performance of the engine. It will seem less powerfull.