Oh I know the Ecoboost might be "rated" to pull that much, but I am more inclined to think 'real world' situations. Remember, that is a 3.5 liter V6. Until that engine is proven, I wouldn't be pushing my luck if I owned one. A close friend has the new Ecoboost, and is pulling a 6500 lb (dry) KZ fifth, and while he says it pulls fine, he definitely knows the camper is behind him. He drives semis quite a bit, so that comment tells me that he feels he is pulling enough weight at 6500 lbs.
My Flagstaff is 7500 lbs dry, and it is just about right for my F250, as there are definitely times when I am very aware of it being back there.
Yes, we could all pull at max weight under ideal conditions, but what happens when conditions are not ideal? I have seen more than a few drivers come in off the highway with the blood drained from their faces and a look of shock in their eyes. I would prefer to not go there.