I have gotten contradictory mileage reports on those motors. I have heard the ecoboost is as high as 22 mpg, but i have heard 17-18 mpg out of them too, same with the 5.0. Everyone that has booth motors say that they have more power than the old 5.4.
I did witness a ecoboost in a crew lariat race a raptor with a 6.2 in it, and the ecoboost won.