Tires for A6 4.2
I have a 2001 4.2 and tried many tires. The car actually comes from Audi with Performance Summer Tires. Useless in snow so get All seasons.Toyo tires are inexpensive but give rough ride and didn't last more than 20K Miles. Continental makes a the Extreme Contact with decent ride and good Winter traction. The best ride so far was Michelin Pilot Sport, but they are $250 each. I got over 40K wear from them.
The new Continentals are rated at 540, so overall, I recommend the Continentals.