The only downside for me on E85 is I change my oil very frequently and the cold hard start is pretty damn annoying. But other than that I love it.
Are you guys running 100% E85 or a blend? I run 25% E85 (4 gallons) on my Speed3 and top off the tank with 93 octane. That's considered pretty safe on that fuel system - most folks haven't run into any issues. The folks running 100% E85 are the ones who run into problems. Even with just 25% E85 the tuner was able to bring on a healthy dose of power for me (+12% increase in TQ).
Very curious to see what E85 can do on the Shelby.
Cons from my experience:
(1) Closest E85 to me is in South Carolina (1/2 hour away)
(2) Prices did go up recently. It was more expensive than 93 octane if memory serves.
(3) 1-2 MPG worse fuel economy