These domestic companies claim they want to "one-up" the foreign automakers, yet they're going in the wrong direction. Sure, 426 hp may sound good on paper, but when 426 hp is motivating 3900-4000 lbs, it's not all that impressive. Take an LS1 car that weighed about 3400-3500 lbs, and was seriously underrated at 305 hp. They were probably making more along the lines of 350-360 hp. These new Camaros aren't any faster. The power/weight ratio isn't much improved, and if it is improved, the serious lack of aerodynamics negates any type of advantage anyway.
Look at the Nissan 370Z. Sure, IMO it's in a different class than the Mustang, but for some reason, they're considered "competitors." The 370Z LOST nearly 100 lbs, gained more power, and is aesthetically better than the 350Z in every way. The price increase was minimal. Lighter weight and more power make a better car.
There is no reason that a mid-sized sporting machine should weigh 3600 (GT)-4000 lbs (Shelby) as an AWD family car like the Fusion (3800 lbs). There's just no excuse for it. The big, fat Taurus weighs 4300 lbs. It's a full-sized machine, and it only weighs 300 lbs more than a Shelby? I just find that extremely disturbing.
In regards to gas mileage, all these companies claim they're trying to improve upon it. I question what types of engineers are working for these manufacturers. Anyone with a head on their shoulders knows that weight will be a large contributing factor to gas mileage. It's simple physics. Instead, weights continue to go up, then 4 cylinder engines are being stuffed under the hood. These 4 cylinders aren't any better than the V6s they're replacing in terms of gas mileage. The smaller engines are working harder to move these behemoths, which is counter-productive to any sort of fuel mileage gain that may be achieved by their smaller size and efficiency.
IMO, the Mustang needs to shrink down in size, but keep its classic styling. The "big Mustangs" of the very early 70s (1971-1973) were a bit frowned upon, and the way things are going, these ones are also going to be.