FYI 85 octane is our "regular" at Denver altitudes, 87 is mid grade and 89 premium. There are a few places around town that sell 91, but you just don't need it. At this altitude again with the engine getting less O2 per CF it is like reducing your cylinder compression, which inherently reduces the chance of knock...which is all higher octane is for.

Ethanol-free gasoline is best used if you are going for total range on a tank. It will get you further than the emissions-friendly diluted stuff. It's one of the reasons I chose to use it in my bike so I could go maybe 150+ miles up in the mountains without refueling (gas is 30-50 cents higher in most mountain towns - some due to tourism, some to actual transportation costs to remote areas). So if I can go further on "cheap" lowland gas, it's worth it to me sometimes.

Flex fuel vehicles that can run on gas or E85 (worst marketing decision ever) can see as much as a 20-25% range (it might even be more - I am recalling another Road & Track article) hit by using a full tank of E85 over gasoline. That's a big deal if you're a rancher or oil/gas-field worker out in the middle of nowhere for extended periods of time.

At least we don't have any complicated factors to consider when buying gas!(removes tongue from cheek)