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Audi's A6 Avant is the biggest-selling premium estate car, and this new fourth-generation car offers more interior space, greater economy, lower emissions and better performance than the model it replaces.

It's light for its size, thanks to the extensive use of aluminium alloy in the body construction – though it doesn't have a full aluminium structure like the bigger A8. Audi says the A6 weighs around 20% less than a conventional steel-bodied car, and that translates into performance, economy and CO2 emissions figures which are tough for rivals to match.

The biggest seller in the new range will be the 2.0-litre turbodiesel engine with 177PS, which can be mated to either a six-speed manual gearbox or Audi's Multitronic automatic, which has a variable ratio rather than a series of fixed gears. Next up is a 200PS 3.0-litre V6 turbodiesel with Multitronic, and there's a 245PS version of the same engine which comes with quattro four-wheel drive and a different automatic transmission, the seven-speed S-tronic dual-clutch gearbox. Top of the range for the moment is a 300PS 3.0-litre petrol V6 with quattro and S-tronic, but a twin-turbo 313PS diesel is due in February 2012.

All the A6s impress with a tidy, tastefully-trimmed cabin which offers leather and satnav as standard. The diesel engines are quiet and smooth, with performance ranging from acceptable (in the 2.0-litre) to distinctly rapid (in the more powerful of the two 3.0s), while the 3.0-litre TFSI is faster still but pays an inevitable fuel consumption penalty. The Multitronic automatic's variable ratio suits the V6 turbodiesel well, making for swift and unobtrusive progress, while cars with the S-tronic dual-clutch transmission have fast, smooth gearchanges. All models have the Audi Drive Select system which tunes the steering, suspension and engine response to your taste. We'd leave it in 'comfort' mode, which gives the best ride and most consistent steering feel. 

The A6's options list is so long you can easily double the basic price of the car: we'd go without the Bang & Olufsen stereo at an eye-watering £6300, or the £2500 20in alloy wheels and low-profile tyres (which look fantastic but generate a lot of road roar). The adaptive air suspension is worth having, however, as it adds a polish to the A6's ride quality.

The new A6 Avant is comfortable, capable and capacious: Audi's domination of the premium estate market looks set to continue.