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Ford:'Use 87 octane even at high elevation.' In 2005 87-octane Corolla, 85 OK?

Ford: “We do not recommend the use of gasolines labeled as “Regular” that are sold with octane ratings of 86 or lower in high altitude areas.”

Corolla Owner’s Manual instructs to use 87 octane or higher in our four-cylinder engine.
It does not discourage using 85 at high elevation. (Denver octane ratings: 85, 87, 91. Occasionally 89 is found.)

Would 85 octane be OK at Mile-High Denver?
Or is better performance and less fuel consumption (if any) worth the increased co$t?
Thank you.
(later edited)

Yes

+1 for Uncle Turbo. I used to live in the high desert of Arizona. 85 octane works just fine.

No…At Denver’s elevation, getting ANY car to spark-knock is quite a challenge…Ford is worried that the computer, sensing the elevation and advancing the timing to compensate will produce detonation on 85 octane gasoline. Paying $.20-$.30 cents a gallon more for 87 octane is a rip-off and offers consumers little or no measurable benefit at 5300" above sea-level…I doubt Ford made the effort to actually test these vehicles at high elevation to see how they operated on 85 octane fuel…But they must run just fine on it because that’s what 90% of them are fed…

The owners manuals for my Lincolns call for 91 octane and using 91 has never made one iota of difference in performance, fuel mileage, or anything else.
I frequently travel to the mountains of Colorado through places like Independence and Cordova Passes, Leadville, Rocky Mountain National Park, etc. and have never had even a hint of a problem with 85 octane.

If the EGR system is working fine and there is no pinging involved then you should be fine.