Well, I ran a bunch of tanks of premium, but I needed to fill up yesterday, and I mixed in some E85.
I filled with 6.008 gallons of E85 and 7.985 gallons of 87 octane. It works out to 38.54% ethanol. This will be a great test to see if this is the limit for E85 without a CEL. It's 93.93 Octane.
E85 was $2 a gallon, and 87 octane was $2.60.