2011 a6 gt 52,000 miles, cats went bad (probably due to tune), had the rear axle breather tsb, interior parts such as soft parts on door panels loose. air vents damaged (I believe car wash did that) mechanically its running great. with my o/r x mufflers and tune I pulled a high flow x muffler tune 3.73 m6 11 last night.
Mine-- 2014 GT has 5,000 miles on it now, had it for a year and everything in my sig has been on it for 4500 miles. Runs and rides great.
The wife's-- 2013 GT has 22,000 miles on it, her daily driver. It has Roush axlebacks and sportlines on it, strut mounts are starting to make noise and has a couple of interior rattles. Just got back from scrapin' the coast in it and it got 27 mpg.
2011 M6 3.73 17,900 miles orderd 2010.. Built motor has 3,200 miles of the 17,900. Runs great. Trans whines but thats due to hard launches on sticky tire, shifts like butter and never had any lock out or missed shifts.
2011 A6 GT, 40,300 miles. As far as issues, had Rear end done(whine on decel) and had cam actuator sensor connector break a wire in it. Tuned @56 miles, N2O at <6K, Circle D converter around 7K, O/R X around 32K. Still kicking, no issues(slight decel whine in rear again, guess this one's on me ).
2014 OW A6 @ 5,350 or close to it. I do have whine on decel from 60-50 mph that has been there since I've had it but I've since done suspension so I doubt Ford will fix it. Only other issue was water in the passenger rear quarter panel but it was fixed and cars been great ever since. The temptation to tune it grows everyday but I want to keep the warranty for a little while longer at least.