It's a tough one to answer because the Targa has always been the hardest 911 to pigeonhole. It's neither a Coupe nor Cabrio yet it evidently has considerable niche appeal, accounting for some 10 per cent of total 911 sales in its previous guise. Nevertheless it remains the quirky member of an otherwise well- defined model range.

Early Targas, with their trademark B-pillar hoop and simple removable roof panel, were definitely the ugly duckling of the 911 line-up, but the arrival of the 993 model saw the first appearance of the clever sliding glass roof. This aesthetically superior concept has been subjected to further development and for the first time it's now applied to the recently revised 996.

At first glance there's plenty to suggest that the new Targa is a credible compromise between the Cabrio's sins of the flash and the Carrera's understated, driver-focused character. A clean, unbroken arc of glass and steel runs from A to C pillars, retaining the 911 Coupe's unmistakable profile, even with the huge roof panel retracted. Only the shape of the rear side windows betrays the Targa's identity, and it remains an unarguably handsome car.

Practical too, because Porsche has cunningly engineered the rear window as a liftback, giving unprecedented access to the diminutive rear 'seats', which in truth are useful only for sprogs under the age of three or, more realistically, an armful of shopping bags. It's a neat idea that only adds to the 911's already impressive ability as a truly usable everyday supercar.

That said, it was amusing to see Porsche engineers recoil in horror as the more mischievous members of the UK press jokingly described the Targa as Porsche's first 911 hot hatch.

But the men from Stuttgart can afford to smile these days. After surviving some perilously hard times back in the early '90s, Porsche is now amongst the most profitable car manufacturers in the world. With annual 911 sales at 26,721 units (up 15.9 per cent), Boxster sales at 27,865 (up 8.2 per cent), and the eagerly-awaited Cayenne 4x4 on the horizon, the Stuttgart marque has never been in better shape. Which is one of the reasons why it's able to perform such a thorough engineering job on a niche model like the Targa.

Available in six-speed manual or Tiptronic S forms, the Targa is based on the Carrera's recently uprated two-wheel-drive platform. With 320bhp and 273lb ft of torque, the flat-six engine - now displacing 3.6 litres - is an absolute peach. Its voice is slightly deeper and more guttural than that of the 3.4-litre engine, while its response is more muscular, with impressive reserves of instant, low-rev acceleration.

It still relishes high revs of course, but the build-up of accelerative force feels stronger and more linear through the meat of the mid-range. There's still delicious punch beyond 6000rpm, but now the lunge from 3000 to 5000rpm in third or fourth will see you past slower-moving traffic without the need to slot a lower gear and exploit the top-end.

Mind you, what you need to do and what you want to do are two entirely different things because, given the chance, you'll invariably choose to wring-out the revs and enjoy the instant gratification of the Targa at full chat.

With the roof back, the experience goes up a sensory notch as the gruff exhaust note invades the cockpit yet without the increased buffeting and road-noise of a fully open-air Cabrio.

Cynics might look on the Targa as simply a 911 with a big sunroof, but the overall effect of such an extensive and versatile glass area makes it a genuinely fresh experience. You see and feel so much more of your surroundings than you would in a Carrera Coupe, enjoying a Cabrio-like widescreen view of the world without the dynamic and security compromises of a canvas roof.

To aid roll-over protection and to provide the stiffest possible platform for the suspension, the Targa's roof is reinforced with 30mm-thick high-tensile steel tubing, which strengthens the windscreen pillars and roofline. As a result of this extra tubing, and of course the extra glass, the Targa weighs some 70kg more than the standard Carrera Coupe, tipping the scales at 1415kg.

Although inevitably the added weight has blunted performance slightly, Porsche claims the Targa will still hit 62mph in 5.2sec, 100mph in 11.4sec and 120mph in just 18.3sec, while top speed is an impressive 177mph.

So, are we any closer to understanding the Targa or its buyers? Well, a day's driving on some fine Austrian mountain roads certainly highlighted its undiminished dynamic ability, not to mention its uniquely and engagingly involving interior. As to who will buy it, I'm still none the wiser. As a purist, I prefer the single-mindedness of the Carrera Coupe, and I'm not sure the Targa's roof aperture is sufficiently alfresco to satisfy a Cabrio fan. But because the Targa remains much more than an uncomfortable halfway house it's impossible to knock it, especially as you can go from snug, flush-fit, zero- wind-noise mode to fresh, zero-buffet open mode in just 8sec. ί¿½

The one cloud in the Targa's otherwise azure airspace is Mercedes' new SL, complete with its fully folding hard top. This Merc offers the integrity of a Coupe, the versatility of the Targa and the ultimate open-air thrills of a Cabrio in one slick, brilliantly engineered package. Despite Porsche's claims that Targa and SL customers will be very different animals, it's only natural that there will be some crossover.

If the buyer's genes comprise more poseur than purist DNA, the multi-tasking Merc probably has the edge, but the Porsche is the better driver's car.