THE Audi S5 Sportback is a little bit like the sporty kid who makes the state squad for athletics only to find out that their cousin has been chosen to carry the national team flag at the Olympic Games.

No matter how good the 245kW five-door Sportback flagship – and it is laudable in almost every dimension – it will still be viewed through a prism coloured by the forthcoming ballistic 331kW V8 Audi RS5 Coupe that is due to arrive in Australia in October, ready to poke the BMW M3.

Of course, the supercharged V6 S5 Sportback is not meant to be compared with a super coupe whose V8 power curve is still heading north at 8000rpm and which no doubt will be accorded an equally stratospheric price tag, but journalists on this week’s S5 Sportback launch who had previously sampled the 2010 RS5 in Europe had a common refrain: “The S5 is excellent, but you should drive the new RS5 ...”

But no matter what, the $129,300 S5 Sportback will have two advantages over the RS5: greater practicality and a way keener price.

This third and final S5 model is designed to address a conundrum: Why should car buyers who enjoy a fun drive have to compromise on doors and large lumps of practicality?

Or looking at it another way, why should car buyers who demand practicality matched with high performance be forced into something like a luxury two-tonne SUV with attendant high fuel consequences?

The low-rise Audi S5 Sportback seeks to bridge those gaps, making a commendable fist of all of them: performance, practicality, sportiness and efficiency.

And it does all that with a modest persona, hiding its light under a bushel of mild body enhancements – so mild that only keen Audi spotters are going to pick this German Q car by items such as quad exhaust pipes and chrome bars on the grille. Of course, the menacing red-backed S5 badges should be all the warning you need …

At the heart of the S5 Sportback is the powertrain that starts up the front with a longitudinally-mounted supercharged direct-injection 3.0-litre TFSI V6, continues through the latest, seven-speed iteration of Audi’s S Tronic dual-clutch automated gearbox and on through Audi’s quattro constant all-wheel-drive system.

Put them all together and you have a driveline that could be hung in the New York Museum of Modern Art.

Audi has had three decades to perfect this all-paw system – the first Audi Quattro was unveiled at the Geneva motor show in 1980 – and in the S5, it nears its pinnacle.

Driving the S5 Sportback on a switchback mountain road on a sunny afternoon revealed competency by the bucketload topped by lashings of driver enjoyment.

Plenty of pure-bred sports-cars might have been quicker – think 911 or R8 – but not many – if any – other five-door hatchbacks with V6 power would see which way the S5 Sportback went.

Yes, the driver can tell that this is not a small car, with its stretched 2811mm wheelbase (to accommodate the two extra doors over the Coupe version) and 1875kg kerb weight.

But for the well-to-do family person who is likely to be attracted to this vehicle, the reassurance of well-planted, class-one passive safety is a big selling point.

To that end, this Sportback flagship oozes road feedback that signals the driving boundaries as clearly as a rattlesnake’s rattle. Like other fine German cars, it absorbs punishment such as mid-corner lumps and bumps with barely a murmur of discontent, all the time keeping a little extra grip up its sleeve to cater for idiots (who said that?).

For the uninitiated, the steering turn-in against the natural yaw of the vehicle is a revelation, flat and unflustered with just a hint of understeer at the utter limit.

The S5 Sportback we sampled at the launch was equipped with Audi’s optional $6900 Drive Select dynamic drive system that includes a new, intelligent sports rear differential that can direct more torque to the outside wheel in a corner.

We would like to advise if this system was superior to that of the standard car, but unfortunately when we jumped into the conventional S5, the roads had nary a twist or turn suitable to give it a solid test. That will have to wait for the full road test.

What we can say is the car fitted with the optional system was awesome on the transition from braking into the corner to rolling back on to the throttle, seamlessly hunkering down out of the bends with the calm demeanor of a vicar sipping tea.

We can also say that the system in sports mode adds a little extra sportiness to the controls – the steering, gear choices etcetera – like giving a fine blade a little hone.

The ride quality of this sports-oriented S5 is on the stiff end of the scale, but not hotrod hard. Of course, the Drive Select-equipped car can vary this ride with a push of the button, moving from comfort to sports or even automatic (the latter leaves it to the car to adjust according to recent driving behaviour), and yes, this works, but whether many buyers stump up the extra cash for the privilege is a moot point.

No S5 Sportback driver will have to pay extra from the lovely little burble of the supercharged V6 at idle, which makes red traffic lights seem not so bad.

Fired up, the supercharger atop the engine stays pleasantly quiet – not a whine to be heard – as the V6 snatches fistfuls of revs in an seamless power arc. We had pondered why Audi had dispensed with turbo-charging on this particular engine and elected to go for the mechanical blower, but here is one good reason – zero lag.

Put that engine together with the snappy seven-speed dual clutch auto and Audi’s claimed 5.4 second sprint time to 100km/h should not be a problem.

Purists will bemoan the lack of Audi’s blissful V8 engine note that enhances the driving experience in models such as the S5 Coupe and R8 (“you should drive the RS5 …”), but they won’t be unhappy with the return at the petrol pump.

Audi claims a combined figure of 9.4 litres per 100km, but our drive yielded a still commendable and not-V8-like 11.2L/100km. Less lead-footed progress should better 10L/100km.

The driving experience is enhanced by the first-rate ergonomics of the cabin, with sports seats nicely positioned in front of an appealing, totally practical dashboard with its chrome-rimmed white-on-black dials, chunky leather-wrapped steering wheel and the best cabin plastics on the planet.

Sat-nav and lots of the latest communication equipment is standard, as are gear change paddles mounted behind the steering wheel for the S Tronic transmission.

The firm seats – sportier than the usual Sportback chairs, with beefier side bolstering – are cloaked in black leather and alcantara. The latter in the cars we drove was light grey, which while adding visual interest to the otherwise dark cabin, would pose a challenge to keep clean in the real world.

Rear seat accommodation has ample legroom, but it is back here in the practical department that we question Audi’s decision to fit only two rear seat belts to make this vehicle a four seater. It seems to fly in the face of the practical bent of this hatchback.

The door openings are also hardly huge, which would not be appreciated by mums fetching two-year-olds from the rear seat, but at least head room is commodious in all seating positions – a win in a coupe-like hatch with a sloping silhouette.

Further back, the 60-40 split-fold seats signal the Sportback’s other party trick – voluminous luggage room, with seats up or folded down flat. Try that in your S5 Cabrio.

In reality, we have finally arrived at the nub of the S5 Sportback – its practicality. No one will buy this vehicle unless they have a need to move at least some stuff and regularly carry back-seat passengers.

Nor will they buy it unless they care passionately about the ‘S’ driving experience (afterall, the standard Audi A5 Sportback diesel is more than $30,000 cheaper).

But for those who like to mix their top-shelf automotive tipples, the Audi S5 Sportback might be the tonic.