marks exhaust

So I've been eyeballing exhausts and so far I like the looks and sound of the Marks performance 4-2 the best. It has a nice deep rumble and it doesn't seem deafening from what I've seen on the videos of it. What can I expect in terms of performance gains from these? How do they stack up...

Ive been poking around with the idea of an aftermarket exhaust for a bit now. ive decided to get some feedback on the marks exhaust. i will probably go with the 4 into 2 black ceramic. i do know hes hard to get a hold of, but besides that. what is everyone's experiences with these pipe if...