I'd suggest just getting a turbo back. A cat back is really only for sound quality and a very slight gain in power. Maybe 5hp. A turbo back will net a significant increase, with a tune of course, in over all power output.
The kind is really based on your personal choice, I could recommend something and then 5 other people would recommend 5 other exhausts.
Resident Grumpy Old Man(Keith)
03 SRP 2.34L now with Spec C goodness
08' LGT Gears...