Every year luxury carmakers one-up each other for bragging rights as to which of them builds the most outrageously powerful luxury sedan. While 400 hp was the norm just five years ago, some manufacturers are now pushing into 600-hp territory.

"Clearly these cars are putting more horsepower to the ground than one would ever think was normal for a luxury sedan," says former automotive financial analyst Joseph Phillippi, now a consultant to the automotive industry. "These are Ferraris with four doors and a trunk. The appeal is the exclusivity they offer, the 'I'm rich enough to afford one' statement the car makes, albeit quietly."

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These rare and pricey super sedans are based on popular models but carry sophisticated engine, transmission and suspension technology. They're styled and priced with well-heeled enthusiasts in mind. "I'm sure there are buyers who are clueless, simply spending money because they have a lot of it," Phillippi says. "But most of the people who buy these know all about the car -- maybe even know how to drive it well."

Unlike some gaudy sports cars with huge wings, scoops and obnoxiously loud exhaust systems, these extreme luxury sedans only hint at their prowess -- with a discreet "supercharged" or "V-12" badge on the trunk or fender, a slightly lowered stance, and larger, flashier wheels with low-profile tires. "You're not looking to impress Joe Six-Pack," says automotive consultant and publicist Martyn Schorr. "It's the aficionados who are impressed -- and valets. Valets are used to seeing luxury cars, but they're impressed when they see a Mercedes AMG or BMW M logo."

Visual differences between regular sedans and their superlative counterparts are often so subtle that the average driver will have a hard time distinguishing a regular Audi A4 from the hot rod RS 4, or an elegant Jaguar XJ8 from the ferocious XJR. The kid wearing a sideways baseball cap will never notice the subtle differences ... until you shut him down when the light turns green. "The sedans are stealthy, so you can be a performance loony and not look bad in your neighborhood," Phillippi says.

If you don't have the space in your life (or garage) for multiple cars -- a commuter for the weekdays, an SUV for the family and a sports car for the weekends -- one of these extreme sedans may be ideally suited to your needs and desires. Why not instead commute in a four-door that will leave Porsches and Vipers in its dust, and enjoy cosseting luxury and the amenities of a limo while you're at it? "These sedans work as everyday family vehicles yet deliver performance that was, until recently, reserved for truly high-performance sports cars," Schorr says. "And you can go anywhere and park one. It's just a sedan. It doesn't attract the attention a Ferrari does. They're invisible to all but knowledgeable people."

Super sedans are perhaps the only cars that ask no compromise. There's plenty of trunk space; comfortable seats for four (five in a pinch); no need to apologize for their handling; most have smooth highway rides; entry and exit require neither a stepladder nor paparazzi-attracting contortions; and straight-line performance is spectacular. Plus, a set of good snow tires will turn any of them into year-round cars.

It's no wonder that the market for such extreme luxury sedans is quietly growing. "More and more people have the money," Schorr says. "The difference in price between it and the conventional model doesn't mean much to them. These people also tend to be fickle. Before the car is one or at most two years old, it's sold and they buy another one, so there's a constant, evolving market for them."

Who exactly are these very special buyers? "Guys with high levels of testosterone," Schorr says. "People who already own one or more sports cars. People who truly appreciate high performance and feel they can't be without it in their daily driver."

Super sedans are also arguably safer than are outright performance cars and tend to be bought by more responsible drivers. "The people who own these cars don't go nuts with them," Schorr says. "It doesn't matter that they have 500 hp. They're responsible individuals, they paid a lot of money for them, they transport families and business associates. They're more likely to stay out of trouble than are people who get behind the wheel of something red with two seats and very high horsepower."

Our top 10 list is varied, especially considering this tiny automotive niche. Some are small, stark and nimble, like the Audi RS 4; others are high-performance bargains with a base price just above $40,000 (Chrysler 300C SRT8); while some push well past six figures and are laden with luxury, such as the $180,000 Mercedes-Benz S65 AMG.

We've ranked the top extreme sedans, in ascending order, according to their power-to-weight ratio, which is the number of pounds of the car's total body weight that each unit of the engine's horsepower has to move. Certainly a car's suspension, tires, brakes and all-around handling factor into the performance equation, as do cost and amenities, but the more horsepower you have per pound of car, the quicker and faster it'll be. We excluded the ultra-luxury sedans (Bentley, Maybach and Rolls-Royce), being that they're a different breed and not as focused on performance.

First up and number 10 on our list is the recently released Audi S8. Based on the already impressive full-size A8 sedan, the S8 packs a 450-hp V-10.