Sound too good to be true? Our thoughts exactly. That is until Mercedes dropped off the keys to an E55 AMG wagon, one of the most practical E-classes we've ever tested, not to mention the quickest.

Mercedes quietly unveiled the E55 wagon not at the big-news auto shows in Detroit or New York but rather at the almost-forgotten L.A. show, maybe because it was hinting at the car's "sleeper" nature. Why draw attention to a car that itself attracts very little? This is a wagon, after all, which means it lures about as much interest as that vehicle so associated with motherhood, the minivan. Which is fine by us, because it only makes the stunned looks on the faces of 911 and Corvette owners that much more entertaining.

The only telltale exterior signs that the E55 wagon is not an ordinary E-class are essentially the same subtle cues that differentiate an E55 sedan from an E500—a body kit supplied by Mercedes' tuner arm, AMG, replete with bigger rocker panels and more aggressive front and rear fascias, the former employing a stealthy black mesh grille; 18-inch aluminum wheels that frame monstrous, silver-painted calipers; and the "E55 AMG" and "V8 Kompressor" badges.

Of course, the telltale sign that really matters resides under the hood in the form of AMG's hand-built 5.4-liter, supercharged-and-intercooled 24-valve V-8, which puts out a Jack LaLanne-healthy 469 horsepower and 516 pound-feet of torque. Teamed with a heavy-duty AMG five-speed automatic, the blown V-8 produces staggering results: 0 to 60 in 4.1 seconds; the quarter-mile in 12.5 at 114 mph; and 0 to 150 in 24 flat. The comparisons at the start of this story show what kind of sports cars this wagon stays door to door with. "Mommy, race that Ferrari!"

Moreover, take a look at the results from the last E55 sedan we tested (C/D, May 2003), and you'll notice that the wagon, despite weighing 256 extra pounds, is 0.2 second quicker to 60! It's as if, like a sprinter, the wagon's curvaceous rump is all speed-inducing muscle.

The explanation lies within better weight distribution, which in turn results in a more efficient launch. The wagon carries 51 percent of its curb weight over the rear wheels, whereas the sedan burdens its hind legs with just 47 percent. Simply put, the wagon's rear-driven 265/35R-18 Continentals are able to hook up like two college freshmen, thrusting the "estate" off into the sunset with ungodly authority. The wagon bettered the sedan's 70-to-0 braking—from 173 feet to 171—as well as its skidpad performance, which jumped from 0.83 g to 0.85.

So, compared with the sedan, the wagon is quicker and handles better, and it's way more practical. Although sizable, the sedan's trunk can swallow just 16 cubic feet of cargo, whereas the wagon's huge hold can accommodate 24 cubes, five more than the Cayenne Turbo's. And with the second-row seatbacks folded, storage capacity expands vastly to 69 cubic feet. But if it's people and not cargo you wish to haul, never fear—the wagon can be had with an optional rear-facing third row ($995), the ideal lookout spot for a couple of kids to wave at defeated Evos.