I have added 3 litres of Mobil 1 0W-40 to the engine since the beginning. It is sitting at just over 3200 miles today. They generally take a bit more than usual during break in as all the mating surfaces are still sorting themselves out. I would add oil 500ml at a time. As you know with 911s, you don't want to overfill them.

Of course, I didn't exactly baby my car like many do...

Dan