The cars that are designed to run on E85 are Multi fuel vehicles. They have a sensor in the tank and can run everything from E0 to E100?. They do this by having flexible maps that adjust to the fuel that is in the tank. we don't have flexible maps; we have a fixed tune that creates problems if the properties of the fuel change from what we had in the tank when we got it tuned.
The service stations don't guarantee the ethanol content and they definitely don't guarantee the octane rating (not that the fuel is rated by octane rating), Jeff mentioned that from what he has seen with the E85 tunes there is a definitely a consistency problem in that if a car returns to the dyno he has to change the tunes because the fuel properties have changed from tank to tank.
The scotchers E85 though is guaranteed to be the same every tank, after all it's what the V8 touring cars are running and they need consistency.
It's up to you what you run, at the end of the day it's your engine; but fuel isn't the thing to cheap out on.