I was just reading a thread in the last couple of days where this was debated. I think it may have been an older thread on e90post.
Someone who had them up both up on a lift commented that their labeling and markings on the exhaust system were different. I believe that someone said that the 335is exhaust has the flapper valve and the BMW PE doesn't. I think that it was said that the BMW PE was louder and deeper. The determination was that they're not the same. But I could be wrong.
But the 335is exhaust definitely does sound sweet! I can't wait, it's just weeks away!