I have both a 2011 supercrew Ecoboost and an 2009 supercrew 5.4L. The Ecoboost averages about 19MPG. However, I drive it carefully, nearly all highway. MPG really takes a hit when you start enjoying all the power the Ecoboost has. The 5.4L averages about 14.5.
And, the EB accelerates much harder than the 5.4L, it's not even a contest. A side by side comparison has the EB truck very far ahead in seconds. About 20 truck lengths by the next block.
I hear the 5.0 is more efficient than my 5.4, and faster than my 5.4 too. But, I'm not at all sure the 5.0 will return better MPG than the EB.