Why on Earth would Cadillac do this? Stuffing a 556-horsepower supercharged V8 into a wagon would seem to garner the same sort of mainstream commercial success as Amish Playboy. Who in their right mind would want a wagon with the performance of a sports car?

If you need to ask these questions, then there's just no way you'll ever understand the 2011 Cadillac CTS-V Sport Wagon. Either you think wagons are awesome or you think they're dowdy grandma-mobiles that went out with wood body panels. If you get it, then the CTS-V Sport Wagon tends to elicit the same sort of giggle-inducing reaction as seeing someone clever do something incredibly goofy. Here is a car that has enough cargo room to go antiquing and then enough horsepower to leave the grannies at Ye Olde Treasure Barn coughing in a billowing cloud of white tire smoke.

The Sport Wagon is now the third CTS body style to receive the "V" treatment following the sedan and this year's new CTS-V coupe. As with the other two CTS-V models, the wagon receives a supercharged V8 as well as firmer suspension tuning, bigger wheels, stickier tires, more powerful brakes and V-specific styling enhancements. But the CTS-V has more than just world-class performance going for it; this Caddy also provides an amenable ride for both daily driving and long-distance road trips. Of course, with its generous 25 cubic feet of luggage space with the rear seats raised and 53.4 cubic feet with them lowered, the Sport Wagon is more practical than the whole lot.

In fact, there's no other car sold in the United States that gives you this much practicality and this much performance in one slick-looking package. Like the other CTS-V models, the Sport Wagon is not without its foibles -- its standard seats leave much to be desired in terms of comfort and support -- but for car enthusiasts who get it, the 2011 Cadillac CTS-V Sport Wagon could be the only car they ever really need.

The 2011 Cadillac CTS-V Sport Wagon is a high-performance sport wagon that's offered in a single well-equipped trim level. Standard features include 19-inch wheels, high-performance tires, Brembo brakes, adaptive xenon headlamps, foglamps, a power tailgate, an adaptive and adjustable suspension, keyless ignition/entry, remote ignition (automatic transmission only), a rearview camera and rear parking sensors.

Inside the cabin, standard features include dual-zone automatic climate control, heated eight-way power front seats, driver memory functions, leather and faux-suede upholstery, a power tilt-and-telescoping steering wheel, an auto-dimming rearview mirror, OnStar, a navigation system with real-time traffic and weather, Bluetooth and a 10-speaker Bose surround-sound audio system with a CD player, satellite radio, an iPod/USB audio interface and digital music storage.

Options include a panoramic sunroof, heated and ventilated Recaro sport seats with adjustable cushion and backrest bolsters, interior wood trim and faux-suede trim for the shift knob and steering wheel.

The 2011 Cadillac CTS-V is powered by a supercharged 6.2-liter V8, a slightly detuned version of the engine under the carbon-fiber hood of the mighty Chevrolet Corvette ZR1. It sends a shock-and-awe 556 hp and 551 pound-feet of torque to the rear wheels. A six-speed manual gearbox is standard, and a six-speed automatic transmission with shift buttons mounted on the steering wheel is available as an option.

In Edmunds performance testing, an automatic-equipped CTS-V Sport Wagon sprinted from zero to 60 mph in a remarkably quick 4.7 seconds and ran down the quarter mile in just 12.7 seconds. The CTS-V Sport Wagon's estimated fuel economy is 14 mpg city/19 mpg highway and 16 mpg combined with the manual transmission, and 12/18/14 mpg with the automatic.

The 2011 Cadillac CTS-V Sport Wagon comes standard with antilock disc brakes, stability control and traction control, front-seat side airbags and side curtain airbags. GM's OnStar emergency communications system is also standard. Braking performance is excellent, with the sedan posting a short stopping distance of 109 feet from 60 mph in Edmunds testing.

No Sport Wagon or CTS-V model has been crash tested, but the Insurance Institute for Highway Safety gave the regular CTS sedan its highest rating of "Good" in the frontal-offset, side and roof strength tests.

The fact that the 2011 Cadillac CTS-V Sport Wagon tips the scales at just under 4,400 pounds makes its astounding performance all the more remarkable. The combination of its muscle-bound V8 and modest exhaust note makes the CTS-V deceptively fast. While the manual transmission is a good one, with a nice firm shift action and a surprisingly light and progressive clutch, you'll actually get quicker acceleration with the automatic transmission when it's in Sport mode. However, the automatic is neither the quickest nor the smoothest-shifting unit we've experienced.

The CTS-V's standard Magnetic Ride Control suspension offers a good balance between ride quality and handling via driver-selectable Tour or Sport modes. While it's capable of throwing down some seriously quick lap times at a track, the CTS-V can't hide its 2-ton-plus mass on a tight, winding piece of asphalt. That hefty feeling in tight corners is quickly forgotten when you turn the mighty V8 loose on the straightaways, though.

First, the bad news. The 2011 CTS-V's interior isn't much different from that of the regular CTS model. Now the good news: The CTS already sports one of the nicer passenger compartments in the segment. The overall look is high-class, with an attractive and functional layout for gauges and controls. Materials aren't the best in class, but they're generally high quality. The faux suede seat inserts and steering wheel/shift knob trim are an especially nice touch.

The cabin's most significant shortcoming is a driving position that can be awkward for some, and the standard front seat design, which lacks the comfort and support required for spirited driving. The optional Recaro seats address both of these issues (while adding ventilation to boot) and are highly recommended.

Cargo capacity is obviously important with a wagon (even one with 556 horses), and the CTS-V Sport Wagon provides a generous 25 cubic feet with the rear seats raised and 53.4 cubic feet with them lowered. This is a bit more than the Audi A4 Avant, but a little less than the BMW 3 Series wagon.