Yesterday I was able to bring my S6 to a true 271 Km/h (168 mph)and the speed governor did not come into action. The speedo was at just below 280 Km/h (174 mph) and the rev counter at 6200 rpm in 5th gear, which is how I calculated the true speed. I must add that the road was sloping down slightly and I was at +/- 1200 ft altitude only.
I tried again to 6100 rpm = 267 km/h (165.7 mph) and again to 6000 rpm = 262 km/h (162.8 mph).
About a month ago I took the S6 a few times to 250 km/h (257 on the speedo) 5700 rpm and felt the governor coming into action, but not this time.
I called the Service Manager of my usual Audi dealership and he said he has never heard from anybody that the speed governor vanished without being purposely removed! He also told me that any Audi dealer, or anyone having a VAG computer can remove the speed governor!!! by entering the "00" code in a particular directory.
He believes that mine may have shifted to a higher speed code, or reset itself to "00". I will have that checked sometime soon.
The S6 handled very well at those high speeds. I believe the rear spoiler may have help a bit. On bumps it was a bit loose though...

Andre's Audi Page
Audi Club of South Africa