Great thread OP! Carbon build up is the enemy of any DI engine.
I really want to buy a digital borescope/camera that will work with a N54/N55 motor. I just have not found any units cheap enough - yet. I don't know IF I would use that wire brush that you used. I think I would go with plastic picks so to not scrape the valves up too much. But that is a minor snip-et. I think I would also replace the spark plugs too. You need a special slim 14mm (12point) 3/8th's socket for that.
A good friend of mine(he goes by the user name:
Doldonics on the Audi forum) has an
Audi RS4. His car had only 40K miles when he did his carbon cleaning. He also used BG products - but he removed the intake manifold and let the valves soak for serveral days. Spraying down the valves twice per day... then after a day or two he would use a plastic tool to remove the carbon buildup. He has been using a OCC of his own design... but still he had some carbon buildup - probably from the first onwer of the car. He bought his RS4 used.
RS4 with intake manifold removed...
all buttoned up - custom OCC lower right...
Dackel