The gintani xpipe will give you massive gains, the difference is noticeable instantly even without a tune (to be honest, I never felt that my tune added hp, only the xpipe).
It comes with a couple options - you can either get 2 sets of HFC's or fully catless, and you have an option of getting 2 resonators or 4 as well (depending on your cat set-up). I'm currently running the Gintani catless xpipe with 4 resonators with their sport exhaust and the setup is great. The xpipe (especially catless) will make your car louder than it is now, and I wouldnt recommend the catless setup with the race catback unless you have very UNsensitive ears and a high tolerance for drone and obnoxious noise.
In regards to cats, if your looking to get max hp and performance out of your car the way to go is catless. But if your sensitive to smell (it does smell like shit, but I personally love it) and are worried about emissions (you can always grease someone to take care of your inspection for you) then your best bet is HFC's. Also, catless will be louder than a HFC setup.