Subbing the V6 EcoBoost for the V8 is about providing the same power with more efficiency. Said to be the premium engine for light-duty trucks, the direct-injection gas engine will offer something like 400 horsepower and 400 pound-feet of torque while carrying an EPA rating of "at least 23 miles-per-gallon on the highway." Those power numbers handily beat what you'll get from any of the current engines on offer, even though it's down two cylinders.
The "Coyote" 5.0-liter, modular, four-valve V8 will have "huge heads," and will return the same numbers as the V6: 400 hp and 400 lb-ft. This engine will become the standard F-150 lump, returning the same gas mileage as the current 5.4-liter but with much more power. This same engine will also reportedly find its way into the Mustang. That will leave the 6.2-liter V8 (the Boss) slated for the Raptor later this year as last engine choice (unless there's a 4-cylinder EcoBoost added in 2013), and it will go into special edition F-150s and the Super Duty trucks.