It's not just the bigger tailpipes, there's definitely a different rear silencer I believe. It is louder than the GTI, nothing silly mind you, just makes the DSG gear changes on boost sound lovely.
Also, some GTI owners in Germany have already retro-fitted exhaust parts from the Clubsport (so there must be different than the GTI) although with my limited German I am not sure whether it was just the rear silencer and/or middle resonator.