I hear a hi-flow cat can make a substantial difference in back pressure. Any mod you make to your exhaust system is ultimately limited by the cat.

i dont see it doing much more than a full exhaust set up.........

My previous truck (on the right, obviously)

I has a stainless steal exhaust with a free flow cat, big difference. When the exhaust rusts out on my X I plan on getting headers, free flow cats and dual exhaust.

just curious, why?

depends on where you live. in NJ if it is OBDII you have to have a factory cat or you wont pass inspection.

Its pointless because I beleive there is 3 cats total on the x. 2 pre cats and an after cat.