i wouldn't think "gas" + whatever is in it today, is stoich at 14.7:1 even if its E0 let alone E10.
slightly OT: when i was commuting 3300miles/month i shifted the AFR on my 2.0 breeze to 16.8:1 for about 3-4MPG improvement. I would lean out the closed loop until the downstream O2 tests...