even if you could make it keep up with a new mustang would you really want to drive it everyday? MPGs will likely be 10 or lower, probably no a/c, and you would still have all the issues an aging fox does. The 11 is brand new, gets great mileage, has all the creature comforts, and still has that new car smell.
Why My car makes more than double the power of an '11 GT, still has A/C, powersteering, and got 22 mpg the last time I drove a long distance. Does it have issues? Yes! That's part of the game, though.