I don't really think you can go wrong with either one, either.
The cylinder deactivation seems to help my mileage on the highway, when it's flat, and not windy, and I'm not towing. When conditions are right, I can get 18-19mpg (just for that stretch), which I suspect is better than the Ford with the 6.2. But realistically, I don't spend much time under those conditions. Most of the time, it's hilly, or windy, or I'm towing. Or something. Nice to have, but not significant.
I like my 6.4L a lot. It tows well, and drives smoothly. No complaints, other than the recent recalls Ram has had, none of which have caused problems for me, but have caused trips to the dealer.
E85? For a truck? Not a concern to me. Wouldn't use it even if I could, and if I could find it. In a car? Maybe I'd try it. But not in something I tow with. That's not where I experiment.
Drive them both, and buy what you like. Factor in who gives you a better price, and which has the better dealer. Pick what 'ya like, and enjoy it. Either one will server you well.
Jason, Angie, and our boys, Sean (13) and Liam (8)
Now with Radar and Daisy, both Boston Terriers. Missing Artemus the Labrador, gone on ahead.
2016 Ram 3500 CC Big Horn - 6.7 Cummins - B&W RVK3600 hitch
2015 Palomino Sabre 33RETS Platinum fifth wheel