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I'm going to be the contrarian here.



I know agreement will take the fun out of being the contrarian, but I'll agree in full.
Point 1 - The unscientific explaination for higher octain is that the added octanes delay detonation - This is important in high compression engines to retard pre-ignition, knocking, pinging. If it ain't pingin' you don't need it.
Point 2 - The old notion that high-test, ethyl, premium or whatever you call it is better gas was probably true at one time. There was probably a little more care in the refining. That's not the case anymore - Its all crap, and we buy it as fast as it drips out the end of the pipe. It's all laden with chemicals, inhibitors, detergents, and more fillers than a McDonalds Chicken McNugget.
Point 3 - I religiously check mileage - for no other reason than it serves as your gas gage - I use 89 because that's what's recommended in the owner's manual (yeah, some of us do read them), but have mistakenly used 87, 91, and 93. I have detected no difference in mileage.
Point 4 - (This is just my own theory) There has been some small amount of concern about carbon build-up. If High-test fuel retards combustion, and if it isn't a requirement, I wonder if using higher octane may in fact reduce firing efficiency in lower compression engines and therefore contribute to the carbon fouling that some have experienced. Again, that's just a thought with little to base it on - But its my idea and I'm stickin' to it.