The Audi RS 7 is unlike anything on the road. It's powerful, sleek, and oddly practical. It doesn't easily fit into a particular category. Is it a supercar? Nope — it has four doors and a ton of storage space, two features that supercars typically lack. Is it a supersedan? Sort of, but it has a hatchback like an old Honda CRX. So it's a fun little hot hatchback? No! It's 16 feet long and costs 120 grand. A four-door coupe? Perhaps. When Business Insider got the chance to spend a few days behind the wheel of a 2015 Audi RS 7 4.0T quattro Tiptronic, I was on a mission to figure out what this beast was all about. Audi took the stylish A7 luxury cruiser and handed it over to the mad scientists at the brand's high-performance Quattro division, where they promptly pushed the envelope on everything that car can do. . Quattro replaced the A7's "reasonable" engine with a 4.0-liter V8 and then added twin-turbos for good measure. With an earth-moving 560 horsepower, the RS 7 is the most powerful Audi sold in North America .The engineers also took a scalpel to the A7's pretty-boy looks by installing a full aerokit. The result is a car Audi claims will hit 60 mph in 3 7 seconds, with a top speed of 174 mph (which is limited by the car's computers). The European specification RS 7 can hit 190 mph Incredibly, Audi seems to be under-reporting its performance figures. Car and Driver magazine's RS 7 test car made the sprint to 60 mph in 3.4 seconds, while Motor Trend casually hit 192 mph on Germany's no-speed-limit Autobahn highway with the Euro-spec car. In all likelihood, a pro driver on a test track could go north of the 200-mph mark. Even with the conservative performance figures, the RS 7 is still one of the fastest passenger cars sold in North America. When fitted with Audi's self-driving tech, the RS 7 can lap Germany's Hockenheimring Formula One racetrack at nearly 150 mph without a human driver. As impressive as the RS 7 is on paper, it's even more enjoyable to drive. Which is pretty much crazy From a standstill the Audi zips through the ZF-made automatic transmission's 8 speeds. The car grips like its riding on Velcro tires. Its engine just keeps coming in a never-ending surge of acceleration. And this twin-turbo V8 is enthusiastic about producing power, like a persistent salesman always reminding you he's got more power if you want it. As you rumble down the road, speed builds effortlessly like a rolling tide restricted only by traffic and the law. And when the roads do get bendy, Audi's Quattro all-wheel-drive system, advanced aerodynamics, and electronic stability control make the RS 7 feel as if it's embracing the road, even when pushed a bit on slippery asphalt. This thing is riding on rails! When you finally remind yourself to take a breath and settle into the cabin, you immediately realize something. It's a really nice place to be. In line with other Audis, the RS7 has one of the finest interiors in the business — not just because of the high-quality materials the company has used but rather it's the beautifully rendered LCD, the brilliantly laid out controls and switches, and a bulletproof infotainment system. Not to mention some of the most comfortable seats I've ever sat in. There's even plenty of space in the back for passengers Especially when you fold down the rear seats. This came in handy when I took the RS 7 to IKEA on a rainy Saturday afternoon. The RS 7 fit in perfectly at the store's loading dock. I used it the same way I would a crossover SUV. So with the RS 7, we have the utility of a crossover ... .... the performance of a supercar ... .... the sleek lines of a European sports coupe and ... ... the cosseting feel of a premium luxury sedan. What more could you possibly want Sure, the $106,000 base price is kind of steep, but the RS 7 a product that's truly unlike any of its would-be competitors. The BMW M6 Gran Coupe is incredibly fast and one of the finest sports sedans in the world. But its interior is cramped and it lacks the RS 7's versatility. The Mercedes-Benz CLS 63 AMG is gorgeous and has more power, but it doesn't have the RS 7's cargo capacity. Back to our original question: What is an RS 7? Is it a supercar or a supersedan, a coupe or even a hatchback? It's none of the above. It's an RS 7. It stands alone. Proudly.