Just a note, higher elevations generally have lower octane levels, around where I live, 91 is the highest, some places only carry 89. This is not an issue as detonation becomes less of a concern the higher the altitude due to less dense air (so I'm told).
At sea level, I'd always use 93. Up here I'm stuck with 91, and unless I can't get it out of town somewhere, 89 will never be used. My Hemi asks for 91, and there is a noticeable difference in performance with 89 or 87 octane, though I do run 87 from time to time with no adverse effects.
When I used to travel a lot, my '01 Celica was noticeably more peppy with a lower grade of gas at sea level, it's always good to know those cross country trips will usually end in a better performing car for a week or two.
