Do this little experiment:
Ok I live in a small town in the middle of the mountains so this is what we do for entertainment.
I had a 99 Toyota tacoma, wanted to figure out if the high oct. stuff really made a difference. Ran 3 tanks of the "cheap" stuff and averaged the MPG (21) Ran 3 tanks of 92 oct and averaged the MPG (24) And felt like I could notice the difference in power. If you work the difference in price/gal and figure out how much it cost per mile to run it was cheaper in the long run to buy the high oct. stuff. Told my friend about this and he tried it in his 92 Chevy with a 350 v8, worked the same for him, now runs the 92 oct.
However I tried this with my 2000 Chevy s-10 and my 2001 toyota 4-runner and there was no difference in MPG. Go figure?