i dont see any reason for them not to be the same, a pipes a pipe but im sure there are many ppl here that can correct me on that
as far as the cat goes, its always the most restrictive part of an exhaust system, have a look at it, from the flange its like a bottle neck.
even if u just upgrade the cat itself u will get some gains.
check out this thread http://www.skylinesaustralia.com/forums/in...2&hl=batmbl