MY how it’s grown.

From a decent-size SUV that has traditionally leaned more towards proper off-road capability (by offering a dual-range transmission) than the vehicle that supplanted it as the prestige 4WD of choice – BMW’s X5 – the Mercedes-Benz M-class has, in its second iteration, become something to be reckoned with.

Quite a bit bigger than the original M-class in all directions, the new Benz is also quite a bit bigger than its BMW nemesis in every direction except width, and offers the interior space to go with it.

And, even though the explosive ML63 AMG version is yet to arrive, there are enough engine choices to satisfy just about all SUV needs.

The ML Benz starts with a 200kW/350Nm petrol V6, moves up to a 165kW/510Nm turbodiesel V6 and tops out with a storming 225kW/460Nm 5.0-litre V8 to challenge the 4.4-litre 235kW/440Nm BMW X5 – if not the top of the range 265kW/500Nm 4.8is.

It challenges the X5 on price too, undercutting the Bavarian at all levels except the range-topping ML500, which is about $5000 more than the X5 4.4i (but a lot less than the 4.8is).

Undoubtedly the most generally relevant model is the ML320 CDI which, at $82,900 when launched in September 2005, was just $3000 more expensive than the petrol ML350 and brought the latest turbo-diesel technology to the Benz brand after its initial unveiling in the Jeep Grand Cherokee earlier in the same year.

This 3.0-litre turbo-diesel V6 is arguably the most impressive of a genre that is not lacking technological firepower. The Benz engine produces more power and torque than BMW’s sophisticated, alloy-block 3.0-litre inline six-cylinder turbo-diesel, and probably trumps it in terms of smoothness and silence also.

This is saying a lot, because the BMW engine – available so far only in 530d and X3 3.0d models - is already an outstanding oil-burner with frugality, power and silence rating as major virtues.

But the identical-size, also alloy Benz V6, as fitted to the ML 320, produces more of everything, in terms of power outputs and would undoubtedly be just as economical if it were toting around the mere 1810kg of the X3 3.0d rather than the ML320 CDI’s 2185kg.

Still, an average 9.4L/100km is not to be sneered at, particularly when its accompanied by the surging torque and silent smoothness of the piezo-injected turbo-diesel.

More than any similar powerplant that comes to mind, it banishes smoke, smell and rattle to another, long-past era of diesels.

It does all the things we now expect of a modern diesel engine – instant starting, smoke-free exhaust, low noise levels – but does them all just a little bit better. The typical sounds are most of the time so far in the background it could easily be mistaken for a regular petrol V6 and there’s a smoothness that would once have been completely unimaginable with any sort of diesel.

Combine this with a superlative torque plateau, where the 510Nm maximum comes in at just 1600rpm and sits there until 2800rpm and, of course, the frugal sipping of fuel, and it becomes a virtually unarguable SUV choice.

It has towing-friendly lugging power, as well as the extended cruising range allowed by both the diesel’s economy and the increased, 95-litre fuel capacity.

Underlying all this are the new ML’s deep-seated abilities on- and off-road.

It closes in on the X5 on the tarmac while giving customers the ability to add a good measure of off-road ability.

Specifying the $10,150 Off-Road Pro option adds a 1:1 – 2.93:1 two-speed transfer case, two switchable differential locks for the full-time 4WD, and an additional function in the Airmatic suspension that comes with the pack and enables ground clearance to be raised from the standard ride height to as much as 291mm, helping acquire a 600mm fording depth.

And there’s more.

Following a mini furore over the ML’s being fitted with a space-saver (though fully inflated) spare wheel, Mercedes-Benz quickly followed the vehicle’s launch with an aftermarket option that attached an external full-size spare to the back.

Following that innovation, the rear compartment was then reworked to accommodate an optional full-size under-carpet spare, more than filling the receptacle that held the space-saver and taking up some luggage space – but a welcome modification nonetheless.

The test ML320 came with not just the Off-Road Pro pack, but also with the under-carpet spare. All this worked in our favour because we did experience a flat, having been warned in advance by the ML’s standard tyre pressure indicator.

The bulge in the rear floor was a small price to pay for the convenience of not just being able to replace the deflated tyre with a full-size spare, but also being able to slip it out of the way once we’d changed the wheels.

The ML thus scores points for accommodating what most car companies seem to think of as an increasing irrelevance. It earned our respect, even if the full-size spare is an option.

Certainly the ML320, fitted with the Off-Road Pro pack, is more than competent dynamically. The Airmatic suspension offers driver choice of three basic modes - automatic, Sport or Comfort – and helps the Benz act with newfound precision on the road.

The ride quality is excellent, smoother and better at absorbing small bumps than the new (also air suspended) Range Rover Sport, although – despite the fact it points very well – the Benz is not quite as sharp as the RR in the steering.

But the ML320 is in good company when the chips are down, definitely a brisk, handy device in both highway and urban situations and hiding its more than two-tonne bulk (albeit less than the outgoing ML) very well.

Add this to respectable off-road capability and you have an SUV able to take on much more than its leather and wood-trimmed interior would seem to invite.

The off-road electronics include things like an easily-used selector switch that enables the 4WD system to operate in auto mode, with the centre differential deciding when it’s appropriate to lock, or selective locking of the centre and rear differentials, as well as DSR Downhill Speed Regulation for serious off-road descents, and the ride-height selector.

This is on top of the Start-Off Assist that comes as standard in all MLs and facilitates easy uphill starts, off-road ABS and off-road ASR to minimise wheelspin when taking off on unsealed surfaces.

The good thing about all these systems is there’s no fumbling with levers to bring the functions into play. Just press a switch or twist a dial and your ML is set up, not quite as comprehensively as Land Rover’s Terrain Response system, but ready to rock nonetheless.

There’s a bit of a mix of BMW and traditional Benz in some of the functions. The shift lever for the seven-speed auto is, 7 series-style, located on a steering column stalk yet works surprisingly well, and the parking brake is your normal Benz foot-operated variety. There’s not a console lever to be seen.

The seats, electrically adjusted for height and backrest angle but manual fore and aft, are trimmed with a combination of fabric and fake leather and are big and comfortable. There’s loads of leg-space, and shoulder room, in both front and back.

The rear seat split-folds quickly and easily, forming a flat floor if the cushions are first flipped up and providing a terrific maximum load capacity of 2050 litres – with all seats in place, there’s still 833 litres available.

Being a Mercedes, the M-Class also addresses safety in a non-compromising way.

It incorporates, for example, the Pre-Safe system which prepares for an imminent crash by adjusting the front seats, tensioning the seatbelts and, if one is fitted and the ML is skidding, also closing the sunroof. The ML also gets anti-whiplash front head restraints and eight airbags - including dual front airbags, sidebags at front and rear, and full-length curtain bags.

For the hedonistically minded, the ML320 CDI has been equipped as standard in Australia with alloy wheels, Parktronic front and rear park-assist, Thermatic climate-control air-conditioning, Speedtronic variable speed limiter as part of the cruise control, a multi-function steering wheel, six-CD changer, rain-sensing wipers and mobile phone pre-installation. There’s also a rear cargo cover, and standard roof rails.

The M-class doesn’t show any evidence of the quality issues that bugged the first series. The US-built Benz looks, and feels, totally upmarket inside even before the options box is ticked.

Like the ads say, this is the Mercedes-Benz of 4WDs.