Spy Shot: Audi S6 Avant

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M5 rival: The Geneva Motor Show sees the unveiling of the Mercedes E63 AMG wagon and BMW M5 Touring (see separate stories) - and Audi will have an arch-rival lined up too, the S6 Avant.

550bhp V10: Seen here out cold-weather testing in northern Sweden, the S6 will have a version of the 5.5-litre V10 (550bhp) used in Audi's Q7 off-roader. This is said to have been reduced in capacity to a mere 5.2 litres for the S6, in which it will develop around 440bhp. However, if that's just not quick enough, a full-fat RS6 is on the way a year later, with the 550bhp unit.

19-inch alloys: The S6 Avant will be distinguished by its deeper front grille and airdam, 19-inch alloy wheels and double exhausts; it is also expected to have aluminium door mirrors, not seen on the car pictured here.