If you were going to gut anything, I'd say do the UP or the 3rd cat. The DP is a waste of time, since its still a flat plate. Granted, the cat inside it is restrictive, but the flat plate by the wastegate is too. Go with aftermarket, either long or short. If you go with a shorty (i.e. Stromung DP, very nice and some sell it ceramic coated) and need a catpipe to replace the 3rd cat, I have one. 2.5" and mates to stock DP/catback flanges.