You WILL theoretically pick up power with the E85. I think it was one of the larger Ford V8 engines that had a higher HP rating on E85 than with regular gasoline. This assumes that the engine is calibrated to take advantage of the E85's higher octane, and I am guessing it is to maximize gas mileage if nothing else.

I don't think I would run a vehicle on a steady diet of it, but if I had an FFV vehicle (I have not owned one to date) I sure would be sure to try a tank and see if I liked what I felt. People spend hundreds of dollars on mods for 10 horsepower, and the E85 may give you that for the cost of more fuel consumption (which is a by product of E85).

Good luck,
George