Originally Posted by semtex

Agreed, 100%. Spiderman -- a cat-back exhaust is so named because it's from the cat, back. As in, from the back of the catalytic converter(s) onwards. A cat-back exhaust alone will yield significant results. But to go the extra distance, some people also replace the stock catalytic converters with either high flow cats (HFCs), or test pipes. Test pipes are essentially just pipes with nothing in them. In other words, you're taking out the cats entirely and have nothing to filter out the pollutants. Test pipes are not street legal, fyi. Not that I have anything against them per se. I had Kinetix test pipes on my 350. But this time around, I've decided to go with HFCs and stay 'clean'. Think of HFCs as a compromise in between full-blown test pipes and restrictive stock HFCs. Stillen does not currently have HFCs available for the 370. However, Berk and Kinetix do. If you look at the thread on the Berk HFCs, you'll see that they alone yield up to +19whp, and they alone give you a much nicer exhaust note. Here's the link to DD's group buy thread, which includes the dyno results and the sound clip video:

DDMotorsports: Berk Tech High Flow Cat/Test Pipe Group Buy!

I've decided to get both the Stillen exhaust as well as the Berk HFCs. That should really open up the sinuses, so to speak. Then once I get the CAI put on, we'll really be in business!