Do a cat back. It's easier to bolt up. I'm kinda partial to Mac cat backs. They bolt right in and sound sweet! X pipes have a really loud exhaust drown crusing down the highway, I have a pro chamber from Mac instead of the X-pipe and it sounds great in the car and really good from behind!
Stock cat back pipe is 2.25" and it sure doesn't look mandrel bent to me. You can see where the pipe restricts in the bends.
Most after market cat back systems are 2.5" and mandrel bent (well, not sure about most, I'm sure about my Magnaflow). You can see the difference, pipe doesn't shrink at the bends.
The guy knows what hes talking about. Atleast on the 2004, the stock catback area isn't TOO restrictive. Not as bad as some other cars. Replace the most restrictive areas first. Those being the stock midpipe and the stock mufflers. If you have money for a catback, get a catback. If not, get mufflers and weld them in.