Are you planning on dishing out large amount of boost? If not, then you won't need 3'' exhaust. I'm running custom 2.5'' dp, custom 2.75'' b-pipe/j-pipe (however you want to call it) and 2.5'' JIC catback. My friend is running 3'' exhaust (all the way through) and it drones like a motherf*cker. My exhaust drones too, but nowhere nearly as bad as my friend's lol.