This high flow cat would give you some power, but the real issue is the fact that the first cat is slammed next to the turbo (1.8t) and headers (V6). If you look back 7-10 years you find that auto manufactures had a single cat on the downpipe and it was 12-14" away from the turbo and headers. The problem now is that you can't find an after market downpipe with a single cat ( example TURBO-------c--catback). Manufacturers run dual cat's now because shops won't install a downpipe that doesn't have two cat's on it and some regulation states the cat has to be at the top of your DP. Now if you are, or have a machine shop that will do it for you, you can have them modify a test pipe for you with the main cat on the base and a re positioning of the O2 sensors.

There are articles on the web on the design of this downpipe, but good luck getting somebody to make it and it's a trick to not get ODBII codes thrown with how the current ECU's are designed. But in summery your car does not need two cats. The main cat is enough. Google it and you will find emissions test with a single main cat and it passes all emissions.