Standing next to me in the pit is Bernd Barbisch, lead powertrain engineer. Asked if swapping V8 for straight-six power might have trimmed some of the M5’s inordinately tubby 2400kg or so, he says downsizing was “not an option”. Had they instead used a hybridised version of the 3.0-litre engine from the M3, it would have saved only 50kg. In any case, the feeling in Garching was that a twin-turbo V8 is now integral to the modern M5 character. Fair enough.

Alone, this S68 unit makes 577bhp. Yep, less than the S63 in the old M5 Competition. However, in this state of tune it’s futureproofed for emissions standards, with the motor plugging the shortfall in grunt. Less forgivable is that the overall power-to-weight ratio of the old M5 is still superior. Ouch.

The scale of this new plug-in hybrid powertrain hits home when Barbisch confirms that there was no chance in hell they would have been able to shoehorn it into the old M5, which was hardly an Isetta.

The eight-speed automatic transmission is carried over from the regular 5 Series, albeit with strengthening measures that not only allow for the M5’s top speed of 189mph but that also prevent it from disintegrating when presented with 738lb ft of torque. That isn’t a hollow claim. The torque converter of the old M5 CS was already just about at its limit, and that only had 553lb ft to deal with. The crown wheel inside the rear differential has also grown 10mm and is now of dinner-plate proportions. Its diameter of 235mm is in the world of diffs simply massive, says Barbisch.

Downstream of it is the most expansive contact patch ever lavished on an M5. The 285-section front tyres are the same size as the rears on the old M5 CS; the back is shod with 295-sections. There will be a broad choice of rubber, but dynamics chief Klaus Huber would prefer it if you went for either the Michelin Pilot Sport S 5 or the new Pirelli P Zero R. He says both generate a touch more precision that will be noticeable on the road.

Road impressions will need to wait. For now, we’re confined to the fast, bumpy Salzburgring. Dirk Hacker, BMW’s avuncular R&D chief, leads us out of the pits in an M4 CS. As a PHEV, the M5 has an 18.6kWh battery slung low between its axles. That will yield 40 miles or so of electric-only range and means you will pull off the mark silently. Today the silence doesn’t last long, because Hacker isn’t hanging about.