You don't turbocharge engines for a fuel economy improvement. If you did, manufacturers would have turbos on everything...
And it also proves the real world advantage is that the 3.5 ecoboost provides more torque over a broader rpm range and better mpg than the 5.0L does. This other side argument is silly IMO and I've never heard it argued before that same displacement, same stockish configuration and somehow the turbo engine gets better mpg. 3.5 ecoboost > 5.0L is the real takeaway.
