Well, it's done. For those who didn't see my other thread, I picked up an M3 catback for $100, no more crappy sounding 14yr old muffler. Had to clean up a couple of minor rust spots on the outer casing (nothing serious), and I primer'd it gray. The swap was easier than I was prepared for- the bolts came right off, no problem. But my rear hangers are a little worse for wear, so I gotta replace them soon. And yea- it bolts right up with no modification needed; it does hang a little lower than the OEM, only because it's slightly bigger.
The results? I LOVE this thing! Nice deep tone, not obnoxious at all. I don't know if it's given me better throttle response or if it's a performance improvement at all though, can't really tell yet . . I do know that I've been a little heavy on the gas pedal just to hear it roar
And I'll have to see if it does anything to my gas mileage.
EDIT: I just did some research on this, and the only "mod" that should be done is to change your exhaust hangers to the stronger M3 version. It hangs the same way, but they're built to handle the heavier weight of the M3 catback. Otherwise, I'm told that the stock exhaust hangers will eventually break.