What's all this about?

You're looking at the most-powerful road-going BMW released yet - and, not only that, but the ultimate evolution of the fabled M5. It's called the M5 CS and, yes, it follows the template set by the smaller M2. Whereas we started with that 370hp model, then gained a 410hp Competition version before culminating in the outstanding 450hp M2 CS, so the current 'F90' M5 is going through the development paces. There was a 600hp softly sprung variant to kick us off, then a 625hp Competition and now, finally, there's this.

What's it packing, 650hp-plus?

Erm, no. Peak power has increased by ten horses, to a 635hp maximum. Peak torque remains at 750Nm, same as the M5 Competition... same as the original F90 with 600hp, actually. But don't despair. What BMW has done here is go down the weight-saving route. This ties the M5 in with the previous-generation M3 CS and M4 CS twins, and - more pertinently - by the two 'modern classic' BMWs which really revitalised these two particular letters for the 21st century, the E46 M3 CSL and its M3 CS offshoot.

Extensive use of carbon fibre, much of which you can see draped over the M5's exterior form and throughout its specialised cabin, and the sort of attention to detail that has even seen BMW strip the storage compartment out of the front-centre armrest to save a few grammes has trimmed fully 70kg from the M5 CS's mass, resulting in an EU kerb weight of 1,900kg. It rolls on 20-inch forged Y-spoke alloys wrapped in special Pirelli P Zero Corsa track tyres, while it is also 7mm closer to the deck than the M5 Competition and has the shock absorbers from the M8 Competition Gran Coupe (which rides a bit too firmly for our liking, but we digress). As it's a big, weighty thing, then unlike the M2 CS the M5 CS has M Carbon Ceramic brakes as standard, with either red or gold callipers at an owner's discretion. Power still goes to all four wheels through M xDrive and an eight-speed M Steptronic automatic gearbox, although there is a 2WD rear-driven mode available if you're on track, and this makes the BMW M5 CS outrageously quick for a near-two-tonne limo with seating for four: 0-62mph takes three seconds dead, which is three-tenths up on the M5 Competition, while 0-124mph is done with in 10.4 seconds (scorching) and the top speed is limited to 189mph. Brutal deluxe.

I just need to pull you up on a typo; you said it was a four-seater, but it's a five, surely?

Nope, just four. The rear bench is replaced by two shaped bucket seats, to echo the carbon-backed ones installed up front. On each head restraint is an outline of the Nordschleife, which echoes that early 21st-century fad in which anyone who had been within a 200-mile radius of the Nürburgring then went and slapped an NBR sticker on the back of whatever vehicle they were driving at the time. Further interior signifiers include an Alcantara steering wheel, 'CS' logo on the dashboard and carbon shift paddles.

On the outside, more carbon. It's on the reshaped bonnet, which is entirely made of the stuff but which has some exposed elements near the vents that have been cut into it, as well as clothing the door mirrors, the front splitter, the rear boot spoiler and the diffuser housing the trademark quad pipes. If you popped the bonnet and appraised the 4.4-litre twin-turbo V8 lying therein, you'd see its engine cover was also rendered in, yes, carbon fibre. As to those exhausts, they're finished in stainless steel; and then we move onto the gold. As in, detailing. Not only are the wheels presented in this colour, officially known as Gold Bronze, it further augments all the exterior model badging, as well as the gill bars on the front-wing breathers and the surrounds of the twin kidney grilles. Even the L-shaped Laser light front clusters illuminate in yellow for various functions, rather than white, which is said to be reminiscent of endurance GT racers. And as to colours? Three to go at, which are Brands Hatch Grey metallic, Frozen Brands Hatch Grey metallic (that's matte-effect, obviously) and Frozen Deep Green metallic.

As to the price, the BMW M5 CS will start from £140,780, with first deliveries taking place in the spring. It'll be built in limited numbers, too, so if you want one you'd better move almost as quickly as the car itself can.