Since we are in the summer months, you'd think that the ethanol content of E85 would be higher. But I have not seen evidence of that, no CEL's.
I've decided to increase my ethanol content a bit, going with 4 gallons of E85 instead of 3.5. In the winter, this gave me an occasional CEL, towards the end of the tank and which would clear itself. We'll see.
Gallons E85: 4.000 @ $1.949/ gal
Gallons 87 octane: 8.821 @ 2.249 / gal
Ethanol content of tank: 27.2%
Octane of tank: 90.7
Savings per tank vs. premium at $2.749/ gal: $7.6105