Scan a car's model Range and, if it's one with a seriously strong image, a definitive model will always stand out. With the Porsche 911, it's the entry level rear-wheel drive Carrera, in the Volkswagen Golf Range, the GTi. With the Mercedes-Benz S-Class, that title has, for a very long time, been awarded to the S500. The latest car to wear that badge looks to uphold an illustrious tradition of low-key luxury car excellence.

So entrenched is the S-Class' image as the luxury car yardstick that when testing a BMW 7 Series, an Audi A8, a Lexus LS or a Jaguar XJ it's always to the Mercedes that one turns as point of reference. The sole question needed to assess any of these models' relative success is 'would you buy one over an S-Class?' For years the answer was usually a negative but in the last couple of years, it morphed into a maybe and often a yes. Mercedes' riposte - dubbed the W221 series - is almost overwhelming and the S500 is the model most will look to as the standard bearer of current Mercedes technology and design.

Like many models in the current line up, the S500's badge isn't an entirely accurate indicator of what lurks under the bonnet. An educated guess would be a five-litre V8, but instead Mercedes pack another half-litre of cubic capacity. The normally aspirated 5.5-litre V8 fitted here replaces the old 5.0-litre 306bhp unit and is the first in a series of multivalve V8s that Mercedes have lined up. It'll punch the big Benz to 60mph in 5.4 seconds and hit an electronically limited 155mph. In case you were wondering, the S500's big brother, the S600, uses the same basic engine design but adds a couple of turbochargers to attain its 517bhp power output.

"Buy an S500 and you don't need to torture yourself afterwards wondering if you've made the right purchase. You have"

It's unlikely that S500 owners will feel at all short changed with the 388bhp they have to work with. Mercedes have blown the overtime budget in their quest to combine two seemingly mutually exclusive goals. Not only does the S500 involve the driver such that there's that sense of oneness with the car that is a mark of all the best luxury saloons, but it also manages to take refinement to a new level. Moving away in an S500 feels not so much a function of internal combustion and bearings but rather as if you're skimming noiselessly across a well oiled surface, yet turn the wheel and it communicates.

You have seven forward gears to play with but despite that serious power, the S500 doesn't feel concussively quick. Put that down to a hefty 1,940kg kerb weight and that uncanny refinement which acts as an emollient on many of the usual cues as to rapid progress. Most normal cars can be easily driven by ear, their engine revs rising and falling, wind noise gaining in volume with speed and bump and thump from the suspension signalling when you're really pedalling the car along. You don't get a whole lot of any of this in the S500.

The styling takes a little getting used to, observers like me having grown accustomed to the sleek coupe-like lines of the 'old' W220 generation S-Class. The latest car smoothes the flanks with the absence of side rubbing strips but adds sharply defined wheelarches that some commentators claim are reminiscent of the Mazda RX-8, along with a swage line that runs from the front wheelarch back to the tail light clusters. Bigger in every dimension to its forebear, this S-Class also features a bootlid that's raised. Mercedes claim this mirrors a styling cue from Maybach - their super-luxury vehicle division - but most of the car-buying public will more readily associate it with a BMW 7 Series, which isn't great news when trying to position the S-Class as a trend setter rather than follower.

Most of the underpinnings are constructed of high-tensile steel, and the chassis is a good deal more rigid than the outgoing S-Class, a car which remains a surprisingly entertaining steer. In an effort to reduce all-up weight, the bonnet, bootlid, doors and wings are fabricated from aluminium. The wheel-at-each-corner stance improves cabin space and also helps with engine packaging. Although length of the standard wheelbase car has grown by 33mm to 5,076mm, the wheelbase stretches by 70mm. Opt for the long wheelbase car and the length stretches to 5,206mm, so you may need to get a tape measure to your existing garage! Width goes up by 16mm to 1871mm and the S-Class also grows 29mm taller to 1473mm. This is a car with serious on road presence.

Mercedes' approach in past times with its flagship saloon was to throw a multitude of high-technology features at the design, then wait to see what would stick (a theme continued by BMW's current 7 Series). More recently with the post-'99 version, Stuttgart dropped the gratuitous gadget count in favour of well-judged refinements - and this continues here. The problematic Sensotronic braking system of the E-Class has been ditched in favour of a refinement of the existing hydraulic set-up, dubbed Adaptive Brake. This system incorporates a number of safety features such as the pads lightly skimming the discs during wet conditions and a hill hold function. The foot-operated parking brake, never a hugely popular Benz staple, has also been quietly ditched in favour of an electronic handbrake. Brake Assist Plus can register vehicles ahead by radar and can calculate if the driver is applying too little braking pressure to avoid a collision, powering up the system to maximum retardation. Pre-Safe is another safety system that recognises potential accident situations, tensioning the front seat belts, inflating air cushions in the multi-contour seat to support the occupant and automatically closing the side windows.

Although more people will probably buy the S320CDI than this S500 - in this country at least - the 'five hundred' is still the definitive S Class. It's a car so good that the rest of its rivals suddenly appear clumsy and old hat. The game has moved on. See your Mercedes dealer to find out how far.