It isn’t a sports sedan. It isn’t an SUV. I’m not sure that it’s even a BMW, given my experience of looking at the German automaker’s luxury cars.

This is what the BMW X6 M is: a “sport activity coupe,” or SAC. It’s certainly the oddest segment in the motoring world, outside “shooting brakes” (two-door station wagons) and limos with hot tubs.

BMW has pretty well owned the SAC space, although last year Mercedes rolled out its GLE Coupe to challenge the bimmermeisters for supremacy.

There’s the standard-issue X6, and there’s the X6 M, given more warp and woof (much, much more woof) by BMW’s M performance division. The run-of-the-mill X6 starts at about $US61,000, but once the M dudes get finished with the car, BMW will sell it to you for $US115,000 — nicely equipped, as in the case of the “Long Beach blue metallic” version with “Aragon brown full merino leather” interior I recently tested.

What does the extra $US54,150 get you? Mind-bending, borderline disturbing things, as it turns out. You could buy another car or two, obviously, with the difference. But then you’d be deprived of a driving experience so strange that, well, you’ll feel incomplete. That is, if you need to drive an un-SUV four-door super-coupe that can give you whiplash if you aren’t careful with the throttle and that should inspire confidence going around corners but with a curb weight of 5,300 lbs. and the stance of a draught horse crossed with Optimus Prime, doesn’t.

The X6 M certainly is fun in a straight line, however. The growling, 4.4-litre twin-turbo V8 creates a Matterhorn of torque when you’re tooling around on the highway in the placid confines of gear eight and decide to flick it down five whole shifts to third, squeezing the throttle and unleashing the crazy. This car’s middle name is “GO!”

Breaking up?

Actually, all of its names are “GO!” The g’s come quick — quickest if you’re in “Sport Plus” mode across the board, but fairly swiftly even when you’re in “Comfort.” You’re ultimately not going that fast. But you are accelerating at a borderline alarming pace. It sticks in you head. You’re used to this kind of thing if you’re driving an M4 coupe (I recently drove the convertible version). In the X6 M, the velocity scrambles your thinking. You’re supposed to bond with the furious power of BMW’s M cars. But with the X6 M, I kind of wanted a divorce.

The X6 M is an engineering fever dream. There’s no reason not to treat it like a jolly old freeway cruiser. God knows I tried, making a run from New York City to the Hamptons on the Long Island Expressway (I’ve done this in two Corvettes and a Ferrari, by the way, and they slipped easily into their six-lane alter egos as Buicks). But that unholy turbo V8 in the X6 M taunts you. Slip the gearbox out of manual mode, adjust all the driving settings to the calmest possible modes, order up “Watercolors” on SiriusXM radio, and heck, switch on the cruise control — but no.

The mollified torque still looms like a wild animal stuffed under the hood. The car almost jerks. In fact, it does jerk, like an over-caffeinated panther with fast-twitch muscles. It seems coiled and ireful even when it isn’t supposed to. It put me in the mind of the Incredible Hulk, mid-metamorphosis: It’s almost as if those deeply rational BMW engineers decided to give free reign to something they’d rather not openly discuss. When you pop the hood, you expect to see molten lava. You can’t understand why a fearsome plume of black smoke isn’t coming from someplace.

Bizarre styling

The X6 M looks like a warrior who has showered off the blood of his enemies and slipped into a well-tailored Hugo Boss suit. It looks like it was made by Hot Wheels. It looks vaguely militaristic (it could intimidate a Hummer). All it needs its a cape. It makes an angry sound, its tires are too big and wide and fat, and the styling is thrusty and frankly bizarre. You kind of don’t want to look at it. But then you do. And you sort of wish you hadn’t.

Inside, BMW has done the usual BMW thing and made sure that as the driver of the Ultimate Driving Machine, you feel immediately familiar with the setup. The seat, the steering wheel, the paddle shifters, the instruments, the center console — you’re enveloped in a reassuring, driver-centric BMW-ness. The leather upholstery is supple, carbon-fibre accents are present and skirt that line between stimulating and excessive, and for everyone else in then car the environment is comfortable. Cargo space is adequate, if not abundant.

Mind you, the X6 M is a potent piece of hardware. The V8 cranks out 567 horsepower — over 100 more than the Corvette Stingray! Why? Another 93 equestrians and you’re talking about a Corvette Z06. Add three more hp and you’re got a Ferrari 458. The X6 M does the 550-horsepower Range Rover Sport SVR 17 hp better. This is a mighty Wagnerian poleaxe of a motor. One doesn’t want to argue with it.

Luxury to spare

It also ticks off every imaginable luxury box. The infotainment system is BMW’s and still hard to use, but it does everything it’s supposed to. The sounds system is lovely. The interior styling cues get the “M” treatment, with blue and red stitching on the steering wheel and “M” badges tucked here and there. The seats have many adjustable positions, and they are heated, and they are cooled. The rear seats are quite nice, and the rear climate controls, for what it’s worth, are the best I’ve ever seen.

Still, that engine! With great power comes great responsibility. Under normal driving conditions, you can make use of about a tenth of what I suspect the X6 M can mete out. Nevertheless, as with the Corvette Z06 and the 650-horsepower active volcano many mistake for its powerplant, you aren’t so much driving a car as keeping a leash on the three-headed hound that guards the approaches to the Underworld. Setting it free seems, always, like a very, very bad idea. Plus, it occupies acres of attention span. Daydreaming while driving is not advised.

It’s almost like the Masters of M decided that they just weren’t being taken seriously enough. Too many people had the wrong idea about what a BMW actually is. Remember the sweet little BMW 2002 of the 1970s, that spry and peppy sports sedan that defined what Bayerische Motoren Werke meant to its earliest adopters?

The X6 M ate the BMW 2002 and kept right on chewing. If the dystopia envisioned by “Mad Max” ever comes to pass, expect to see the X6 M among the survivors. The “sport” part of “sport utility coupe,” in light of the X6 M’s overall attitude, seems pathetically quaint. What “sport” does BMW have in mind? ICBM racing? Dodge ball with meteors?

Who would buy this thing?

I simply don’t understand what you would do with a car like this (although when it comes to the regular X6, many customers know exactly what they want to do and are delighted to buy the car, which has been selling well). It isn’t roomy enough to function as an SUV. It doesn’t really make you happy to look at it. Trying to cruise around in it induces anxiety. It doesn’t want you to become one with its bimmerness.

Nothing bad will happen if you take a corner with a bit too much enthusiasm — the technocratic all-wheel-drive system supplies a check — but why would you risk it? It can’t be a family car because is actually something that you keep in the basement and cut loose when the Four Horsemen appear on the horizon. My children fell asleep in the back seat. I thought they were fools.

When I return a test car, especially a high-performance luxury machine, I’m generally a little sad. Not this time. I dropped the X6 M off at the garage. I didn’t look back.

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