Audi's large and phenomenally powerful RS 6 is available only as an estate, and is one of the fastest cars of that type in the world. Based on the A6 Avant, it has a turbocharged 4.0-litre V8 petrol engine producing 552bhp, yet it's also very practical, with a large amount of luggage space.
The list of rivals is shorter than it might be, since BMW does not produce an estate version of the M5, but the RS 6 does have to contend with the conceptually similar Mercedes E 63 AMG estate (offered with two power outputs either side of the Audi's) and the less powerful but still very quick 5.0-litre supercharged Jaguar XF Sportbrake.
Performance
Four-wheel drive helps to give the RS 6 the greatest standing-start acceleration in its class. 0-62mph takes 3.9 seconds, compared with slightly over four seconds for the Jaguar and Mercedes. The top speed is limited to 155mph, though this can optionally be raised to either 174mph or 189mph if you feel the need.
Maximum power is generated at 5,700rpm, but the engine can perform strongly across a very wide rev range - 172bhp is available from just 1,750rpm. On light throttle the engine is very quiet. Push the pedal about a quarter of the way down and you'll start to hear a threatening rumble which turns into a tremendous roar at high revs. The only gearbox available for the RS 6 is an eight-speed automatic with a beautiful shift quality.
Ride and Handling
It's difficult to imagine getting into trouble in any public-road situation
In a reversal of the usual situation, the RS 6 has air suspension as standard and more conventional coil springs as an option. The air set-up is easily good enough for the job. In conjunction with the four-wheel drive system, an electronic differential lock and well-chosen tyres, it gives the car an outstanding amount of grip and as near a perfect front-rear balance as makes no difference. On a test track, we've found that the RS 6 can accept full throttle unbelievably early in a tight uphill corner and stick to the intended line without so much as a chirp of protest from any of the tyres. It's difficult to imagine getting into trouble in any public-road situation. A car with this much performance needs mighty brakes, and the RS 6 certainly has those. Even if you have achieved great speed, the car can lose it very quickly when required. Ceramic discs are available as an extra-cost option if you plan to use the brakes hard on a regular basis.
Interior and Equipment
Along with the RS 7 Sportback, this is the second most powerful RS model Audi has ever produced. The previous RS 6 had 20bhp more but was slower and less economical.
To put it politely, Audi is consistent with its interior design, and the inside of the RS 6 won't come as a great shock to anyone whose previous experience of the brand is limited to driving an A1. It's attractive enough, though, with the usual Audi sense of high build quality. With the rear seats in place, the luggage capacity is 565 litres, rising to 1,680 litres when you fold them down. This is slightly more room than you get in the Jaguar, though there isn't much in it. Neither car comes close, however, to the much more practical Mercedes. The Audi comes as standard with a lot of equipment you'd expect it to have for the price, such as leather upholstery, multi-adjustable sports seats, LED headlights, satellite navigation and a fine Bose surround sound system, but unfortunately no spare wheel. There are of course many opportunities to spend still more money on optional extras.
Cost
Combined fuel economy is 29.4mpg - not bad for such a high-performance car
Without any extras, the RS 6 costs £78,790, slightly more than the less powerful of the E 63 AMGs but significantly cheaper than either the Jaguar or the other Mercedes. Combined fuel economy is 29.4mpg - not bad for such a high-performance car but at the same time probably not an indication of what you'll actually get. Of more practical interest is the 223g/km CO2 rating, which allows the RS 6 to sneak into Band K for Vehicle Excise Duty, leading to annual payments of £290. The significance of this is that although the Mercedes, with either power output, runs the Audi very close, it's in Band L, which means a VED cost of £490. The Jaguar has a much higher CO2 figure and will cost £505 per year to tax. The Audi has no advantage in terms of Benefit In Kind taxation, since all these cars are already rated at the maximum 37 per cent.
Our Verdict
If you want a very fast estate there are not many cars to choose from, but they are all splendid in their different ways. While personal preference and brand loyalty will no doubt play their parts during the process of making a decision, the slightly lower running costs and the four-wheel drive system (for its contribution to simply extraordinary handling) will make a very strong case for the RS 6 among people who don't mind which premium badge they're associated with.