I have owned a Superformance for 3 1/2 years and am very happy with it. You can't beat the bang for the buck. I bought mine two years used with 1200 miles on it. If you are patient you can find a perfect used one for much less than new. On the advise of one of the best dealers I know of, the Olthoffs in North Carolina, I went with a 550 HP 408 CI Windsor stroker. They seriously race these cars, and that is the same basic engine he races. If money were no object I would probably have a 700 HP stroked 427 and the high winding 408 Windsor, and love both. When I first bought the GT, I mentioned as incredibly fast as it is, you don't get near the sensation of speed and near death experience as when driving the Cobra wide open. I absolutely love both cars. I would add if money is not a huge issue, from my research, go with the Kirkham or alumimum Shelby. Thats my 2 cents of advice.
Rick