From what I've read over the last year, mmaturo has had the worst experience, thankfully covered by warranty. My assumptions are that a combination of hard driving and poor quality replacements/mechanic work caused the issue to be so bad. Luckily I've only had the TC swapped on mine and I'm third owner at 92,000 miles now. I'm putting a good amount of extra power into the car and know that one day the trans will pay for it. That said I do my best to care for it without too much flogging. Rebuilt the TC right away with ACE. My drive to work is about 3 miles city, so I can get away with reducing wear and saving the hard driving for weekends.
mmaturo, I wonder if you would have had them rebuilt out of pocket it might have been worth it and kept you in the RS6? I'm guessing you expected the problem to be fixed though, that's a bummer of a story. All that time down must have been a pain, but looks like you've got some good car options.
When/if the trans goes, get a rebuild that is stronger, along with the TC. Sounds like that has been good to many folks. I've heard a few people talk about our trans still being a "normal" one, so rebuild isn't too crazy, certainly nobody wants to spend $5k for rebuild and labor. A rebuild or new trans on a newer M5 is $10-15k, we don't have it so bad. Personally I think the shifting is great for an auto, certainly acceleration! And tip mode gets the job done on back roads.
I had the TC covered by the dealer, or at least $2k of it, and put another $4k or so into various repairs in the last year. Many of these repairs should last a long time, and the beast has been great. Although I've got a cv or control arm clicking on occasion in the front, my car seems to like eating cv joints