The piping is 60mm or 2.36" for you metrically retarded. I would suggest a Thermal 3" turbo exhaust for running that much boost. Also, the WS2 isn't a good choice because the piping is coated mild steel, so it will rust quicker than a full stainless exhaust like Greddy SP2. You also want a straight through muffler design like diablo mentioned and the WS2 is chambered.

It will definitely be an upgrade from stock, but it will restrict exhaust flow at that boost level, so something bigger like I mentioned is probably a better choice.

You should also be worrying about either a test pipe or high flow cat and a wide downpipe as well to eliminate any bottlenecks in exhaust flow.