I've just gutted my two front cats (because they both crumbled into the secondaries, previous thread) and removed the big rears, and welded in 2 stainless bodied metal core 200 cell cats, and it sounds excactly the same as the car on that clip. I've also got an X pipe and through rears BTW, and jesus, it runs so much smoother and more responsive now too.
My mate owns an MOT garage and tested my emmisions after the work.............................yaaaayyyyyyy all good. So why are thet fitted with 4 horrible great restrictive things then ? more for sound emmision than pollution if you ask me.