I would use what you can seperately but wouldn't hesitate to mix them if your 6 / 6 didn't work out to even oil changes.
I am running 5 quarts of the gold with 2 quarts of the green. I have about 3000 miles on the oil.
My car runs great with GC.
Now if I can find some German made Goodyear tires my BMW will be very excited!