IF you are a little confused about exactly what Saab is offering in its present performance-car line-up, join the crowd.

Today, the Swedish importer is offering quite an array of sporty variants, from the thundering Viggen to the entry level 9-3 TS from the limited edition Monte Carlo models (actually discontinued) to the latest incarnation of the renowned Saab Aero badge, covering both 9-5 and 9-3 models.

The confusing thing is, where there was once just one Saab Aero model, there are now five - three based on the 9-3 and two on the 9-5. And there are two engines: A 158kW 2.0-litre in 9-3 models and the 169kW 2.3-litre Viggen powerplant in the 9-5.

Undoubtedly the most impressive in the latest Aero range is the 9-5. Where Saab has been struggling (with the Viggen) to make the front-wheel drive 9-3 chassis contain and control the torque produced by a full-blown 2.3 turbo, the 9-5 has little trouble.

Known as a very competent, supple performer since its introduction in 1997, the 9-5 sports a nicely balanced front- drive chassis that benefits from a few extra years' design expertise when compared to the ageing 9-3.

And in the worked-over form in which it appears in the 9-5 Aero, it contributes significantly to the making of an extremely competent, entirely pleasant executive express.

A performance version of the 9-5 has been a long time coming and the final arrival of the tricked-up, screwed down and wound up Saab could be seen as something an anti-climax - from a visual perspective at least.

Like all other variants of the big Saab, the Aero fails to clearly identify itself. Only the hunkered-down suspension and bigger (than all other 9-5s expect the top of the line Griffin) wheels provide any clue that what you are looking at is the fastest Saab this side of a Viggen coupe.

The story inside is much the same with only a special leather- trim steering wheel, ventilated front seats (also in Griffin), a power sunroof and a turbo boost gauge distinguishing it from the rest.

A closer look will reveal there's a new, automatic dimming rear view mirror, a chunky, leather-topped shift knob for the manual transmission and a button for the traction control system. Gear from the SE model includes leather seats with power adjustment in the front (plus driver's memory), wood grain instrument panel and centre console, dual-zone climate control air-conditioning (with glovebox cooler), trip computer and usual 9-5 touches like the twin sun visors, central ignition key and night panel instrumentation to minimise driver distraction after dark.

Otherwise it is the same, passenger-friendly astrosphere found in any 9-5, from the base 2.0-litre model upwards, with plenty of stretching space front and rear and a conservative but distinctive presentation augmented by fine attention to detail.

And the special gear that qualifies it for the small and barely noticeable Aero badge on the flanks just ahead of the front doors?

Obviously, the chief motivating force is the full-blown 2.3-litre engine - the latest, low-friction Saab powerplant with a 350Nm mountain of torque and a solid 169kW. What is particularly interesting - and this is an ongoing phenomenon from the Swedish car-maker - is the engine speed at which the torque is produced.

If you think 1900rpm is an impressively low speed from which to produce maximum twisting power, then you will be impressed with the 9-5 Aero because this is exactly what it does. And it holds that 350Nm through to 4000rpm.

It does even better than that if asked. In manual transmission cars as much as 370Nm is available as an over-boost, 20-second surge of power if the driver tromps on the accelerator.

The innards of the turbo engine have been treated to some attention, basically aimed at strengthening the more stress-prone areas like pistons and connecting rods. Emissions are attended to by not one, but two catalytic converters that help allow the car to undercut by huge margins even the most stringent worldwide requirements.

The chassis work involves lowering the suspension by 10mm and slotting in larger anti-roll bars, heavier springs and shock absorbers. Grip is attended to by 225/45 Michelin Pilot tyres strapped to 17-inch alloy rims.

And the braking system, to cope with the increased grunt, has been given larger front discs, up from 288mm diameter to 308mm, working in with the 9-5's four-channel anti-lock system incorporating electronic brake distribution.

So the basic, sound, 9-5 essentials have been gently manipulated, creating a car with a distinct sporting edge that nevertheless manages to retain the refined composure intrinsic to big Saabs.

The Aero has a crispness missing from regular 9-5 models. It is more responsive to steering input and even more assured when committed to a g-force inducing cornering manoeuvre, yet it still offers a smooth, quiet ride.

The engine is a blast. Smooth, quiet and always ready - provided it is above 2000rpm on the tachometer - to sweep most traffic quickly behind. Red line and ignition cutout loom quickly in first gear while second gear produces a dizzying rush forward.

Third and forth are for surging past traffic on the open road while fifth is a cruising gear that still produces decent acceleration as long as the car is ambling along at more than 100km/h.

The manual shift is probably as good as any other large supercar but still tends to be notchy in action and is not helped by an engine management system that shuts off fuel during upshifts in a way that makes smooth, full-throttle shifting difficult. Acclimatisation to the car helps though.

Unlike the 9-3 Viggen, the 9-5 Aero does not suffer from significant torque steer. It will tug at the wheel when accelerating in first or second gear with steering lock applied, but with none of the viciousness of its smaller sibling.

And there's a traction control system in there too, working both on the front anti-lock brakes to redirect torque to the wheel with more traction, and on the engine management to wind back output if both wheels are spinning. In the latter case, it does tend to reduce power with a little too much enthusiasm, causing the car to "die" frustratingly right in the middle of a surging accelerative display. Still, it is better than no traction control at all, as is the case in the 9-3 Viggen.

The good thing about the Aero's torque spread is that this very fast car (the 0-100km/h claim is 6.9 seconds, a lot faster than many other so-called sporting cars) is so accessible it is just as pleasant to drive around town as it is on the open road. There are not too many occasions where it bogs down, turbo-like, because the revs are not quite high enough.

So the Saab 09-5 Aero is a refined, rapid luxury car, definitely a desirable and worthwhile competitor for the likes of Volvo's 200kW S80 T6 (which is not as fast as the Saab according to available data) or Audi's A6 quattro and certainly worth mentioning in the same breath as the much more expensive yet slower BMW 528i.

As with other models in the 9-5 range, the fast Saab's biggest problem is its lack of visual distinction. Although the subtlety of the car - there's no rear spoiler for example, only discreet side skirts and new front and rear bumpers - is appropriate for luxury car buyers.