[meford4u]

We are about to embark down the road to a changed exhaust ourselves, with the same idea that you have, increased hp without the noise.
With the many inquiries on here and the phone calls/emails I have made, I found that the shorty header/hi-flow cat/ 2.5" flex pipe is going to give you the same results as the race header, that doesn't have a cat, without the noise.
Time will tell if it's true.
From what I have learned, the larger the flex, the better the increase. You can get smaller flex pipes, but I went after the biggest that would work from Trubenz.