By the way, most here have assessed that 7.5k intervals for BMW's are about right (if a little conservative). That is why your BMW owner's manual has a stamp-box in the maintenance record for an "intermediate" (or some such expression) oil change.
That recommendation is scaled back even further if you are talking about a 335 or a 535 with the twin turbo engine. Because of heat and fuel dilution issues, even less miles recommended. If it were mine, I would probably be changing in the 5k range.
I am using GC in my 330ci based on UOA's and analysis by Terry Dyson. He feels that I have found my oil in the GC, and if you are running a normally aspirated BMW inline six, my own view is that you couldn't do any better than GC.