My vehicles, 2012 and 2108 Highlanders, require 87 octane fuel, i.e. “regular”. In the DFW area regular is 87 octane. On trips to Colorado, regular in the Texas panhandle is 86 octane and in Colorado it is 84-85 octane. I believe the difference is due to altitude. I pay the extra 30 cents per gallon to meet my car’s requirements. What would happen if I bought regular instead? How are octane and altitude related? I am glad I just visit the area. Buying the higher priced fuel on a regular basis would get expensive. My daughter buys regular for her Honda Fit and says it doesn’t have any power.
The logic behind 85 octane in CO is that at higher altitudes cars without turbos, like yours, don’t get as much air in the cylinder, so they don’t need as much octane to prevent pre-ignition. All those CO cars seem to get by just fine on regular. That’s what I’d use.
Toyota is who to rely on for this question, but when I lived in Colorado I used whichever was “regular” as both of my vehicles called for “regular” in their owner’s manual. I expect that would work for you too. It’s true that both engines seemed a little less powerful in Colorado than here in the SF Bay area. But I don’t think that had anything to do w/the octane. I’ve used higher octane here on my Corolla to see if it would help pass emissions. It didn’t. And it didn’t have any noticeable effect on engine power either.
In the way of compensation for lower engine power in Colorado, when I played golf my golf balls would go considerably further in Colorado than California. They’d really fly there, compared to here.