FASHION is a cruel, cruel mistress – just ask any coupe owner who’s had one for more than a couple of seasons. She’s ruthless!

So you can imagine our surprise when BMW sent out an invitation to drive the MY10 update of its six-year old E63/4 6 Series Coupe/Convertible. Just how long has it been again?

Oh dear! 2004 was a long time ago – Little Britain ruled, Mark Latham didn’t, Lost In Translation found huge acclaim, we cut loose to the Scissor Sisters and everybody thought Ford might finally topple Toyota (let alone Holden) with its new world-class Territory.

BMW too was on a roll – or was it a Bangle – with its controversially reimagined 6 Series coupe and convertible.

Underpinned by the E60 5 Series sedan, the 645Ci Coupe and Convertible proved to be a viable alternative to the overtly sporty Porsche 911 and creaky (but striking and sumptuous) Jaguar XK8.

The German four-seater masterfully walked the middle ground between the two, while offering a look as newsworthy as, well, Janet Jackson’s infamous wardrobe malfunction at the ’04 Super Bowl.

But in the hour just before the harsh light of the new decade’s dawn, the 645Ci’s successor, the 650i, seems more Osama-era than Obama-era.

Not only has BMW moved on stylistically, so have most of the flame-surfacing imitators.

The 650i’s very 5 Series-ish dashboard also seems dated, even though 2007’s E63/4 refresh saw the inclusion of the brilliant iDrive II interface from the new 7 Series. The door cards, shiny hard plastic trim and overall ambience just seem old – especially besides a 740i, ironically enough. The latest BMWs show us how it’s done.

On the other hand, although we never liked the fact that the 6 Series Coupe’s rear side windows do not retract, and that it has a big fat B-pillar, the Convertible saves the day with its an open pillarless look with all four windows (and the rear screen) retracted.

Big praise is also provided for the 650i’s 270kW/490Nm 4.8-litre engine – it is simply one of the world’s best V8s.

Mated to ZF’s excellent six-speed automatic gearbox (surely this is enough forward ratios for any car!) it provides the 650i Sport Coupe with massive forward thrust that is served with a substantial side of silken refinement at the same time.

The official acceleration figure of 5.2 seconds for the 0-100km/h time is testament to just how forcefully strong the BMW is, and how the speed just keeps on piling up. By the way we love the way this 4799cc behemoth of a motor will rev to a tad under 7000rpm!

And here’s another thing – not-horrible fuel consumption figures are for the taking thanks to a range of eco-measures like the Brake Energy Regeneration system introduced to the MY10 models that bring a worthwhile 6.8 per cent cut in thirst. Our 10.5L/100km reading after some spirited mountain-road meandering is not too bad at all.

But the 650i’s steering refuses to get into the sports car mood, feeling too remote for a driver to feel totally connected. This is perhaps the biggest disappointment in a BMW, particularly when you factor in just how much grip, poise, precision and control is available to be exploited.

Yet strangely the 650i never seems to shake off its hefty size and weighty feel, so tight turns are not as relaxing as they should be because the driver is always conscious of how much road real estate the BMW needs.

Slotting the auto from Drive to Drive Sport, and pressing the Sport button that tightens the chassis, focuses the steering and handling characteristics significantly, but – again – the 6 Series today trails the best in this department (911).

And then there is the fidgety ride and tyre noise from the Bridgestone Potenza 275/35R19 96W rubber fitted to our test car … it can become tiresome after a while – and it gets worse in the Sport/Drive Sport modes.

So, five and a half years on, the 6 Series Coupe and Convertible range has not quite aged as gracefully as we had anticipated.

Plus, the surprising dynamic irritations (you can’t really call them faults) manage to undermine both the 650i’s luxury as well as sports car aspirations. Capable? Sure. Relaxing? Fun? Not really.

But don’t despair, BMW fans, for the Bavarians do have a solution or three.

The exquisite M3 is almost half the price but more than twice the fun the upcoming 5 Series GT looks promising indeed, while the 7 Series is a grand tourer par excellence.

These days, all offer a more fashionable take on the grand touring theme than the past-its-prime 650i.