First off the Mustang is small enough, chopping off a couple inches isn't going to lose that much weight, take a look at the 1 Series vs the 3 Series, they didn't save that much in weight by making the 1 series smaller. The other thing is that 2014 standards are fleet standards, and not that much higher then they are now, the standards are still figured by the old MPG standards, not to mention only about 20-25% of Mustang sales these days are V8 models and the new V6 gets nearly 4 MPG better highway then the current 4L V6 in it (which gets the same MPG as the 2010 GT)