batmbl is 1st rate trader no complaints. I had a 3inch turbo exhaust end-to-end, and for compliancing purposes, a stock cat was fitted.
I purchased the Catco Metal cat 3inch, with 5inch barrell, to the amazement of my mechanic it bolted on no dramas.
I am sorry to say but it made no difference in performance for me. (Apart from the exhaust my car was stock).
Noise wise, it was exactly the same loudness both, before and after the cat refit.
Maybe if I do further mods like ECU refit, Side mount, and up boost, and fuel, might it help...But sorry in my experience to date, it just didnt do anything for me?