Just wanted to add my $.02 as I've got this dp/mp and the cat-to-axle-back pipe on my car. I had it welded directly to the Prodrive axle-back (easiest way to make it fit, now I have a 1-pc catback). Install was a breeze, everything mated up fine. I got the cats in the dp and mp although I think I would've opted for just the cat in the mp if I had the chance to do it again. I actually just got my car registration renewed a couple weeks back and our state requires emissions and it passed fine w/this exhaust on.
Performance gains were noticeable from the get-go and the sound is very nice w/the Prodrive.
No other performance modifications of note. Just removed snorkel and K&N filter.
Also, figured I'd post a pic of it side-by-side w/its stock counterparts...