In my experience, GC is better than the BMW 5W30, but the BMW stuff is pretty good.
My dad's 540 used OCIs half as long as the standard interval, sees lots of highway miles and isn't driven in an exciting manner. With the dealer oil at 80,000km it sounded like a diesel - low end knock, lots HLA clatter etc... When freshly changed it was a little better, but sounded like [censored].
On my recommendation he tried GC (since I like it in my E39) and it was like a transformation. He also did a round of ARX later and that cleared everything up.
Now he's extended the OCIs a little bit and its quiet right to the end.
With a 335 your principal concern will be oil degradation due to fuel dilution. There are many threads on this topic with DI engines, not just the BMW twin turbo.
If I had a shiny nearly-new car with a DI engine, I'd seriously consider some UOA sampling and Dyson analysis to determine the interval for YOUR engine, YOUR climate and YOUR driving habits. Changing it often is probably going to be more important than whether you use GC, BMW, Amsoil AFL or another oil. Also, be sure that while under warranty you use a BMW LL-01 or LL-04 oil - not one that is "suitable for) those standards. I wouldn't take chances with your engine warranty, especially until the longevity of these units is determined.