I would cancel the 100 cell cat and get in touch with Garry Curley from Piper and see what he can do for you. A straight through centre section won't gain you any more power, only noise. I would enquire as to the cost of a 2.5 inch cat-back and a 2.5 inch custom downpipe inc. 200 cell sport cat from Piper.
I have been through a number of exhaust combinations and before the SC, the best combination that I had was a Milltek 2.5 inch cat-back and a 200 cell sport cat with the precat removed from the downpipe. This gave me a very healthy gain in torque.