I'm still running the stock cat but have thought about replacing it with a free-flowing one from Random Technologies. I've held off on that upgrade for now seeing that it might set off a check engine light and the gains do not seem to be huge considering the cost and the possibility of added noise. But if you are concerned with exhaust noise, I'd recommend against swapping out the stock cat for an aftermarket one--the stock cat acts as a good silencer in itself.

Oh and don't worry about the whole "sound absorption" thing, most if not all aftermarket free-flow exhausts rely on resonators to silence the exhaust note. If, after installing your exhaust, you still think it is too loud then ask the muffler shop to just add another resonator. Initially, on my car, the muffler shop put in one large resonator and I complained that it was too loud. So the following week, I brought it back in and they redid the entire thing for me for free and instead of just one big resonator they managed to squeeze in two smaller ones and now I'm comfortable with the noise level. To be totally honest, I really think the IPD exhaust is a bit overpriced--my total outlay for my custom exhaust including labour & taxes was around $600 Canadian (about $400 US)--huge savings!