i'm wanting to upgrade my exhaust on the a6 2.7t year 1999

i've had people telling me to put on rs4 downpipes and cats(supposedly very good), they are 60mm 2 1/4 inch bore. can anyone tell me what size s4 downpipes are and standard on 2.7t a6's, and which would fit best, i've been told to fit s4 downpipes not rs4, now this is awfully confusing with no actually information or experienced advice

as for catback, where do i start, i've been told rs6 catbacks, which are huge 70mm each side and miltek, which i'm not sure on size.

anyway i have a mate with a pair of rs4 downpipes and cats used i can use. please any help putting this puzzle of mine together