Get the GT-40, it cools and looks better than the Cobra and it makes a few more horse over the Cobra stock, BUT, ultimately the Cobra upper can be ported to outflow the GT-40, forget the box uppers as they are for high rpm use mostly, but really only the dyno would tell which is best for your package.
One benefit of the Cobra is it's much cheaper than the GT-40, and like I said it can be ported.
