I have an 03 cobra, bought new and it is still in good shape. I can sell the cobra and get a 2011 gt500 or keep it and get a 2011 gt. Have not drove either of the new cars but the new gt looks impressive for the price.
If you can afford the cost of carrying both I'd take the 03 Cobra and the '11 GT. I have love for the 03 and if it's a low mileage nice example that you can keep nice, beat on the more common 11 GT.