Audi’s midsized A6 has long been a well-regarded luxury performance sedan and this year the German automaker is offering it to the U.S. in diesel flavor. Counting the extra-potent S6, there are now five A6 variants available, and the 3.0-liter six-cylinder turbo diesel in the A6 TDI quattro Tiptronic might just make choosing between these […]

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