The new third-generation Audi RS 6 demonstrates all that’s wrong with the latest RS 4 – a car which was launched less than six months ago. Like its smaller sibling the RS 6 comes as an Avant version only, they both come with a V8 TFSI engine, but that’s about where the similarities end.

You see, whereas the RS 6 makes its entrance at the top of its class, the RS 4 appears out-of-date before it even goes on sale. Let me explain.

Audi engineers have been able to reduce the weight of the new Audi RS 6 Avant by approximately 100 kilograms compared with its 2,025kg predecessor – making it around 130kg more than the RS 4.

Unlike the 442bhp/317lb-ft naturally-aspirated 4.2-litre V8 TFSI engine in the RS 4, the new RS 6 is powered by a twin-turbo 4.0-litre V8 TFSI engine with 552bhp and 516lb-ft (700Nm) of torque. That’s 20bhp less than the outgoing V10 RS 6, but with 37lb-ft (50Nm) more torque available between 1,750 and 5,500 rpm.

Despite the slight drop in power, with nearly 8% more torque and less weight, the new RS 6 is actually quicker than its predecessor – covering the 0-62mph increment in 3.9 seconds compared to the outgoing car’s 4.6 seconds.

Top speed is electronically governed to 155mph, but this increases to 174mph when the optional Dynamic package is specified. Opt for the Dynamic plus package and the RS 6 is let off the leash to achieve 189mph.

Perhaps the biggest surprise though, comes from the new engine’s efficiency – while the V10 RS 6 was capable of 20.4 mpg and 333 g/km of CO2 emissions, the new car offers a quite astounding 28.8mpg with CO2 emissions of 229 g/km. To put my earlier point in perspective, that’s 2.4mpg better than the latest RS 4 and 17 g/km kinder to the environment. From a model produced by the same manufacturer but with 63% more torque.. Go figure.

This time around, there’s more to the RS 6 than its engine. Whereas its predecessor felt like a blunt heavy instrument, there’s hope that the third-gen RS 6 has acquired some newfound subtlety.

At the heart of the quattro permanent all-wheel drive system with torque vectoring is a self-locking centre differential with an elevated locking value. There’s also a sport differential fitted on the rear axle, which distributes its power steplessly between the rear wheels for greater agility and stability.

Adaptive air suspension is fitted as standard, although this can be replaced by sports suspension plus with Dynamic Ride Control (DRC) as an option. Whereas the air suspension lowers the car by 20mm, the sports suspension plus system employs steel springs and three-way adjustable shock absorbers, interconnected diagonally by means of oil lines and a central valve control unit.

This is the same principle used on the previous RS 6, which proved either too firm (in sport mode) or too soft (in normal), so it might be worth waiting for the road tests before finalising your order.

Another new system being offered on the RS 6 is Dynamic steering, which allows the driver to steplessly vary the ratio and boost of the steering, via Audi’s drive select panel.

Brakes receive an upgrade with a choice of ventilated steel discs in 390mm diameter or 420mm diameter carbon fibre-ceramic discs. Six-piston calipers are fitted, in either black (for the standard discs) or red (for the carbon ceramic options).

High-gloss, 20-inch, forged alloy wheels come fitted as standard in a seven twin-spoke design, while a choice of three 21-inch cast alloy wheels with either high-gloss silver, polished black or polished titanium-look finish will be available at extra cost.

Along with the usual RS-styling features that you can see in the pictures, Audi are offering two optional exterior design packages – Matte Aluminium or Carbon. The Carbon appearance package, in addition to offering a more stealthy look, exaggerates the styling of the front splitter and rear diffuser.

There’s a new feature to play with in the RS menu of the DIS (Driver Information System) which uses a shift-system, illuminated by green lights which glow brightly as the engine’s revs increase.

As the driver approaches the red line, the lights turn red and then start to ‘blink’ – a gimmick perhaps, but a useful one, given how quickly the RS 6 is likely to hit that red line in the lower gears.

Despite the improvements made to the latest RS 6, Audi has chosen to price the new model around £800 cheaper than its predecessor – at £77,000. That’s still £3,900 more than the identically-powered BMW M5 (which incidentally offers 28.5 mpg and 232g/km of CO2), but well ahead of Porsche’s £123,776 542bhp Panamera Turbo S which also falls behind with its 24.6mpg and 270g/km CO2 performance.

If that’s not enough of a clincher, then you might like to know there’s switchable flaps in the RS 6’s exhaust system, which make its spine-tingling V8 howl even louder at the touch of a button. Order books open in January, with first deliveries in the summer of 2013.

The Enigma that is the latest RS 4 Avant..

When we asked Audi UK back in June why the RS 4 hadn’t made a significant step forward in engine performance, the answer we received was as follows, “We introduced turbocharging back in 1980 with the Audi quattro – we now have turbocharging, supercharging and high rev concepts, each application chosen to suit the character of the car. Clearly each has its own engineering challenges, but the decision was made for the RS4 to go for ‘high revs’.”

I’ll leave you to draw your own conclusions on Audi’s RS product strategy – historically Audi’s RS models have been turbocharged. And are produced as Avant models only.

The second generation B7 RS4 broke this trend and was a great all-rounder (I owned one myself), but Audi enthusiasts have been undeniably outspoken in voicing their preference for turbocharged RS’ models.

The latest RS 6 would appear to prove why that’s the smart decision for a company that likes to express its brand with the slogan, Vorsprung durch Technik (Advancement through technology). I see the progress in Audi’s third-generation RS 6, so forgive me for not ‘getting’ its slightly-smaller sibling.

The enigma will be further brought into contrast next year when BMW launches its turbocharged straight-six M3. By 2013 the brand which invented the high-revving sports saloon will have completed its ‘M’ migration over to forced-induction, ironically the ground that Audi used to own.