I don't really want to go into details that have been given over and over again, but on a N/A 2.5RS, a 3 inch exhaust is quite frankly way too large. 2.25 is about as large as you'd want to take it. If you're planning on going turbo at some point, you might want 2.5, but anything over that is pointless unless you're going for some heavy exhaust flow, which would require pretty extensive engine modifications. The only other reason is looks/sound, and well, to avoid insulting anyone with my personal opinions I won't touch that one.