The snappily-titled BMW M760Li xDrive is the quickest, most powerful and most expensive BMW ever built.

We’d forgive your scepticism, for little about this plain white limo suggests a particularly fearsome performance machine. It would be like being told that Kerry Packer was Australia’s greatest sportsman; he was definitely a physically imposing presence but nothing suggested an elite athlete.

The M760Li has an equally imposing presence. In long-wheelbase guise it measures an immense 5238mm end-to-end with a 3210mm wheelbase (an entire Kia Picanto is 3595mm long), which provides sufficient space for the rear-passenger-side occupant to enjoy business class-style executive seating.

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Helping keep the champagne in the glass are air springs and active anti-roll bars that offer an incredibly serene ride in almost all circumstances; Sport mode improves body control at the expense of some bump absorption but even so it’s extremely comfortable.

The driver is equally well-catered for with seats that do everything bar your tax return and more toys than Legoland – adjusting the volume with a twirl of your hand using gesture control might be a gimmick, but you’re guaranteed to use it more than the buttons on the steering wheel.

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With such an outrageous level of grunt, it’s just as well that the M760Li is the first BMW sedan on-sale in Australia to feature all-wheel drive. With all four tyres gripping, BMW claims the 2180kg M760Li fires to 100km/h in 3.7sec, making it the quickest BMW ever (until the new M5 arrives), while the top speed is electronically-limited to 305km/h with the M Driver’s Package.

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We’re not expecting it to sound like a 1990s F1 car, but aside from a hint of V8-like burble down low it sounds little different to BMW’s 3.0-litre turbo six.

In corners the M760Li composed but heavy; the Bridgestone RE001 tyres (245/40 front; 275/35 rear) simply aren’t wide or sticky enough to control this amount of car moving this quickly. You’re able to cover ground at a staggering rate, but nudge up against the limit and while you can move the rear slightly by trailing the brake, eventually it will fall into understeer.

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This unusual, slightly confused mash-up of abilities neatly sums up the M760Li. It’s built to appeal to a very specific buyer and we suspect those buyers will absolutely love it; it’s very fast, very comfortable and very exclusive.

However, it’s no better at being a limousine than a $200,000 cheaper 740Li nor, bar its searing speed, is it any better to drive – the brakes are soft, the steering lifeless and it carries an extra 410kg in the corners. And the constant intervention by the various assistance systems is annoying enough to have them switched off in short order.

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Or, if you really want a fast 7 Series, there’s the 447kW/880Nm Alpina B7, which is cheaper, more exclusive, every bit as quick and comes complete with a V8 soundtrack.

2017 BMW M760Li xDrive specs Engine: 6592cc V12, DOHC, 48v, twin-turbo Power: 448kW @5500-6500rpm Torque: 800Nm @ 1550-5000rpm Weight: 2180kg 0-100km/h: 3.7sec (claimed) Price: $425,000