I believe the A6 also comes with the 2.7 liter bi-turbo engine, over 250 horses! I know it comes in the All-Road, but it has a very decided taste like the Volvo Cross-Country. I think the S6 has it too, but not sure about plain jane A6 models.
I have owned a couple of the 1980s Audi's and they are bullet proof cars, in terms of drivetrain, suspension, body (galvanized way before anyone else, now mostly aluiminum). They are very comfortable highway cars, very easy to drive, very quiet, way too fast in the snow! I would NEVER own an Audi without the quattro system or a turbo engine, they are the absolute best at this. You have to look at the people who own Audi's too, I worked at an Audi/VW dealer for a few years and the Audi's were decidely beaten by their owners, they were ignorant and drove very fast (I DO NOT mean any insult to any Audi owners out there, just my thoughts), therefore the cars went through a whole lot more then most people demanded of their car. The downside of the older Audi's was the power options, they were unique and under designed, prone to frequent failure (MB climate control-sound familar).
The new Audi's are at the top of their game, way ahead of anyone else for the all wheel drive, aerodynamics, price vs features. I would take the Audi over the VW, the dealer service must be much better.