Remember the poor old Aston Martin Lagonda? Well, keep it to yourself. Not content with first making it the most unreliable car in its history and then last year exhuming its name to append it to a concept car of breathtaking ugliness, Aston Martin has now bestowed the ultimate indignity upon its 1970s anti-hero: as of now and officially at least, it no longer exists.

I know this because Aston Martin describes this Rapide as the first four-door sports car in its history, thereby neatly excising all those painful memories of the Aston that no longer dares speak its name. But you can see why; this Rapide is as beautiful as the Lagonda was hideous and as well finished as the Lagonda was loosely assembled.

But how good is the Rapide to drive? As good as – let's aim high here – a Porsche Panamera Turbo? The answer is now known, because over one weekend and many hundreds of miles on road and track alike with Stuttgart's sledgehammer in close company, the much-awaited, sorely anticipated Rapide has bared its soul.

This was always going to be an epic confrontation, made all the more intriguing by the fact that for it to happen at all, both manufacturers have had to stray far from their traditional comfort zones into areas unknown by Porsche and conveniently forgotten by Aston Martin.

But most beguiling is that despite the narrowness of the brief – both firms set out to build high-performance, front-engined sports cars that look like coupes but function as sedans – the two vehicles are so different in design and execution. Porsche decided to place the colossal weight of its engineering know-how behind the Panamera, because it could. So, the Turbo comes to market with forced induction for its direct-injection, 4.8-liter V8, plus a seven-speed dual-clutch transmission, four-wheel drive and a state-of-the-art information interface.

Truth is, Aston Martin couldn't build a car like that even if it wanted to. Now, as ever, it appeals on more traditional level to a more conservative audience, with a conventional 6.0-liter V12 breathing at atmospheric pressure and transferring its energy to the rear wheels alone through a normal, six-speed automatic gearbox. As for the on-board electronics…let's just say the Rapide's navigation system is complex.

But at least it's an attractive chattel to park outside your house, something only those employed in Zuffenhausen might rush to say about the Porsche. The Aston only looks a little strange because your judgment is unavoidably informed by knowledge of the DB9, and leaves the impression that the Rapide is the result of one being heated up and gently tugged at either end until the desired interior package was achieved.

Judged on its own merits and to these eyes at least, it is not less than gorgeous. As for the Porsche, even really quite ugly cars usually become easier on the eye over time, but not the Panamera – or not yet, at least. To say the light cast on it by running side by side with the Aston is unflattering is to grossly understate the truth.

Still, the Porsche puts a devastating escape strategy under your right foot. Look at the headline figures and you'll conclude there should be little to tell between the cars; the 493hp Porsche has a little more power than the 470hp Aston, but a touch more weight with it.

But these are not the numbers to focus on. Imagine instead the effect on real-world pace of the Panamera's 516lb ft of torque relative to the Aston's 442lb ft, and of the fact that it generates it at 2250rpm, fewer than half the revolutions required by the Rapide to provide its lesser urge.

We discovered that even on a wet track the Porsche would consistently bludgeon its way to 60mph in substantially less than five seconds – with four large guys on board. You'd need to push the Aston off a cliff before it could do that in the dry.

But do not equate being outpowered with being outmaneuvered. The news Porsche won't want to hear is that the impeccable behavior of Aston's most recent new offering, the V12 Vantage, was not a one-off.

In fact, the Rapide suggests Aston's chassis department has had something of an epiphany. No longer is eight out of 10 good enough; the Rapide's chassis feels as if has been honed until no further detectable improvement was possible. It rides more firmly than the Porsche, but with no greater harshness. Aston Martin has ruthlessly exploited the potential of the Rapide's extended wheelbase to deliver the right blend of primary body control and secondary ride resolution for such a car. Yet at the other end of the dynamic spectrum, it will execute some of the most elegant 100-yard drifts you have ever seen.

More relevantly (albeit less amusingly), this excellence is underpinned by steering that is bizarrely communicative given the Rapide's weight. It may be only 44lbs lighter than the Porsche, but when you're out there running hard down the length of a decent back road, the Aston feels to be carrying closer to half a ton less heft.

Here the Panamera's numerical advantage is not enough. Yes, it's quicker in a straight line, better braked (at least with the test car's optional ceramic rotors) and decisively grippier than the Aston, but step into the Porsche after a good run in the Rapide and it feels like you're driving while wearing oven-proof mitts.

We discovered this along the length of a mountain road in Wales. It was narrow, more suited to a Lotus Elise than brutes like these, and it showed in the starkest terms how a bit of confidence can more than make up for any comparative deficiency in shove or grip. By being that bit easier to place and conveying precisely the nature of the changeable conditions underfoot, the Aston had no problem at all keeping up with the Panamera, while amusing and enthusing its driver in a way the Porsche would not even recognise, let alone be able to emulate.