The Audi RS7 Performance is a vicious $152,000 supercar wrapped in a luxury sedan

Since the German automaker first introduced it as the Sportback concept at the Detroit Auto Show in 2009, and later produced the hulking, four-door, four-passenger car in 2010, I saw the A7 as the red-headed stepchild of the Audi brand. You'll have to excuse the clichéd expression, but I was not a fan.

The A7 was long like an asphalt-bound freightliner, the steeply-raked roofline and the abrupt rear end gave the appearance of a squatting, hump-backed brute. Its dour rear fascia — the taillights and rear bumper collectively — had a sort of perma-grimace to them, like a bulldog.

It's an odd car in an Audi line that is internationally renowned for graceful European design. For me, the A7 was a car that never should have been made.

But another version of the A7 changed my mind. Audi Sport, the car maker's racing division in charge of pumping a select few Audi vehicles with extra everything, transforming them into muscular road torpedoes dripping with horsepower, performed such a treatment on the skeleton of an A7, producing the twin-turbo, eight-cylinder, 605-horsepower RS7 Performance.

Audi recently sent me one in Panther Black Crystal for a weeklong test-drive. I figured this might be the one to change my mind.

Oh, my.

The RS7 Performance is the fastest and fittest member of the A7 line, but unlike the A7, it's built by the Audi Sport racing division. "Performance" isn't just a name here, it's part of this car's DNA.

The Performance model we drove cranks out 605 horsepower and up to 553 pound-feet of torque — a bump from the 560 horsepower and 516 pound-feet of torque in the "entry-level" RS7.

The price difference between the base RS7 and the RS7 Performance we drove? About $37,000.

Those 605 ponies launch the RS7 Performance to 60 mph in 3.6 seconds, according to Audi.

The RS7 retains the regular A7's standard shape. It's still a hulking sort of thing, still awkward-looking — but in this color, with these 21-inch wheels, painted in high-gloss black, it starts to look meaner ...

... and when you're not pretty, maybe mean is the way you get respect.

So, what's it like to drive a car this big and powerful and mean?

Let's hop into these Valcona leather and Alcantara-wrapped sport seats and find out.

You're greeted with more leather and Alcantara, and lots of carbon fiber here in the driver's seat.

The RS7 Performance's dash and center console have a monochrome aesthetic, typical of high-performance sports cars. Our tester had all the tech features you would expect in a six-figure Audi, including a small digital display in the gauge cluster and screen atop the center stack. Audi's Virtual Cockpit will show up in the new model, in 2019.

Remember what I said about that monochrome aesthetic? Yeah, I wasn't kidding. Our test car also had the optional Alcantara-lined roof. That'll be an extra $3,000 if you'd like to enjoy one yourself.

Despite being the most extreme RS7 you can buy, the car is surprisingly quiet and composed on the road. It absorbed the mixed Los Angeles landscape: sometimes smooth and unbothered, most times craggy, unsettled, and jarring — with ease. Even with these 21-inch wheels.

Power delivery is equally as smooth. The RS7 Performance seamlessly transitions from a docile highway cruiser to a vicious supercar when you switch into "dynamic" mode, using the drive-select button, seen on the steering wheel.

It scoots to 60 mph in 3.6 seconds, according to Audi. The 8-speed automatic transmission produces a distinct, guttural "burp" between shifts, which can be heard from the signature large, oval-shaped exhaust outlets typically seen on Audi RS models.

There's some cargo space, too.

Again, this is a very large car, and you'll get a clear sense of its heft when it's parked in a standard American garage ...

... but you'll feel virtually none of that weight from the driver's seat. The RS7 Performance handles like a nimble supercar and seems much smaller and lighter than it actually is. A marvel of German engineering.