Pure ethanol has approximately 2/3 the energy content (per gallon) as pure gasoline. So the "10% more gasoline in your tank" is not the correct way to figure out the effect of 10% ethanol. All you need to know is that E10 has about 97% the energy content of E0. If the E10 you use has the same Octane as the E0 you are comparing it to, there is no reason why you would get 10% better gas mileage on E0 (pure gasoline).You can expect exactly 10% better gas mileage because there is exactly 10% more GAS in your tank. The alcohol doesn't do a damned thing to help the car go forward.
I've kept a detailed spreadsheet of every tank of gas I have put in my car for 5 years like religion. Without any shadow of a doubt, I got 10% better mileage, different octanes had zero effect.
Here's a bit of the accumulated data:
Avg MPG 28.11 Total Fuel $ $4,675.54 Miles Driven 48,117.48 Cost per Mile $0.70 Total Gallons 1716.44 Avg Cost/gal. $2.73 Repair/upgrades $8,244.55