Would a turbo really make that much of a difference? I would think it's only going to impact MPG when you really use it during acceleration.
I wouldn't think highway mileage would take much of a hit.
from what I've been told by several guys who have F150's with the twin turbo charged ECO Boost, when they can manage to keep the turbos out of the picture, them get much better mileage .... the problem seems to come from the truck being much more fun to drive when they kick in the turbos