What about all the advice you can find through a Google search? Wherever I look (outside this forum), the only reason to go uptown on octane rating is if your engine is experiencing knock -- premature combustion of the fuel. And if you're getting engine knock at the recommended fuel grade, then you should be taking your vehicle in for servicing. Engines with higher compression ratios sometimes get away with lesser-grade octane if they have working knock-sensors and/or you're driving gently. Higher octane inhibits gasoline from combusting too easily under higher compression; It has no fuel efficiency or power benefits.

I'm not sure if gpsman1 can qualify his statements about ethanol. It's the opposite here, where regular grade gets the highest average percentage of ethanol additive while premium has none.