[Van5280]

In Colorado, we have 85 as a regular, 87 as medium, and 91 as a premium.
I'm curious folks from Colorado which gasoline you are using in your Gen4?
As for myself i did use the 85 and 87 and couldn't see much difference, not in performance or engine sounds. I'm using Costco gasoline as they are premium tier. ( they only have 85 and 91) and King Soopers gas stations for 87.
I’m getting 33.2 on regular and 33.8 on medium (AWD)
What did you use or what was your experience?

 

[Velox003]

I don't live in Colorado but I would only use 87 due to the recommendation.

This article touches on 85 octane.

Selecting the Right Octane Fuel (fueleconomy.gov)

What is 85 octane, and is it safe to use in my vehicle?
The sale of 85 octane fuel was originally allowed in high-elevation regions—where the barometric pressure is lower—because it was cheaper and because most carbureted engines tolerated it fairly well. This is not true for modern gasoline engines. So, unless you have an older vehicle with a carbureted engine, you should use the manufacturer-recommended fuel for your vehicle, even where 85 octane fuel is available.