I have a stillen s/s exhaust I got at the last stillen open house for $100
It did substantually increase the sound of the exhaust, though I have a CAI and Y-pipe already, so thats to be expected. It has a nice deep sound, but can be a bit droning at times. I've heard the quitest exhaust is the APEX-I WS, which I've found for sale many times on
www.groupbuycenter.com though I'm not sure if any sales are going on right now. For the Y-pipe, I think the hp gains are all going to be similiar, within fractions of hp. A muffler is only going to give you a couple Hp's at best. The JWT will add a little noise to your car, but mostly when you go WOT. The Y-pipe adds the most power and is what I would recomend. BTW, I've driven right next to and past cops here and haven't even gotten a dirty look yet. Sleeper baby, sleeper...
Good luck.