Five hundred horsepower for about fifty thousand dollars - that's what, a hundred bucks a horse?

Meet the new king of the Mustang horsepower - and value - hill, the new Shelby GT500. On a pure power-per-dollar basis, it eclipses just about everything else out there. Each horse will cost you at least twice as much in a Corvette; three times as much in a Porsche. This is some kind of bargain when even a Mustang GT bills out $110 per horse and the V6 model charges $120.

You could make the argument, of course, that this is a Mustang. It's a big car - a heavy car, too, at over 3,900 pounds - and it's arguably a lot less sophisticated than something like a Corvette. It does not have, for instance, an independent rear suspension, or an advanced stability-control system or even a particularly luxurious interior. But then again, that's not what Shelby Mustangs have ever been about: they've been blue-collar heroes, relatively affordable cars that could go out there and dice with high-class sports cars and quite easily hold their own in competition.

Yet despite its size and 1,778-kg weight, as well as sightlines that work a lot better when you don't sit as close to the windshield as I do, the GT500 is remarkably agile and light on its feet, whether you're on the racetrack at Shannonville (where Ford launched the car last month) or on a bumpy, winding road. You turn the big steering wheel, and the car darts more rapidly into corners than it should given how much it weighs. You brush the brake pedal and the car slows immediately. And you hit the gas and get thrown back into your seat as the power comes on and you're hurled at the next curve.

Hey, 500 horses will do that for you. Enhanced by a Roots-type supercharger, the GT500's engine is not just powerful, but it's also very flexible. Torque output is 480 lb-ft, and most of it is accessible from just above idle; the rush of power to the rear wheels is linear, with no peaks or valleys; just a strong rush of forward motion punctuated by brief pauses for gearshifts. Unlike other Mustangs, the GT500 has a six-speed manual; like a Dodge Viper, it's a Tremec T-56, but its shift feel is excellent - nicely damped and easy to use.

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At most road speeds, the engine's sound is slightly more subdued than I expected for such a raunchy-looking car; it's just a bit louder, and barely more aggressive than the Mustang GT. It's only once you pass about 3,000 rpm that the exhaust really starts to blare and the supercharger overlays its distinctive whine over the soundtrack, giving the GT500 an unmistakable aural signature. Whether burbling through traffic or under hard acceleration, the noise certainly turns heads; during a hot spring day, pedestrians gasping though the smog-choked air were still gesturing at me to rev it up so they could hear it (being a gentleman, I had to oblige).

In order to handle all the newfound power, Ford has significantly upgraded the Mustang's underpinnings. While the live rear axle remains, it's better-controlled than in the Mustang GT. The suspension is stiffer all around, of course, and the tires - still 18-inches - are significantly wider all around. Brakes are serious Brembo units - four-piston in front - with large ventilated rotors. The result is a car that feels more nimble and accurate than it has a right to, given its size. There's plenty of road feel through that big steering wheel, the brakes are strong and fade-free, with a satisfyingly stiff pedal under your right foot. And the suspension telegraphs exactly what's going on at the corners without beating you up.

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What impresses about the GT500 is that its stability on the racetrack largely translates into road use. The rear end will hop sideways only if it hits particularly severe bumps in corners, and ride quality on the highway is actually quite acceptable. Only freeway expansion joints hit at just the right speed and angle to upset the car. On the track and on winding roads, the fast Mustang felt progressive and stable: very easy to drive. The big Goodyear F1 Supercar tires provided ample cornering grip, and the overall ride quality was impressive, with only small amounts of lift under acceleration and nose-dive under braking. There was very little head-toss in side-to-side transitions, which bodes well for the GT500's road behaviour. Reasonable control efforts help as well: the clutch and steering actually feel lighter than in the regular GT, and the throttle has a nice progressive action.

Mustang enthusiast Andrew le Bret, who drives a highly-modified 1989 Mustang LX 5.0 - and who's first on the list at his local dealer for a new GT500 - told me after a brief drive that he was surprised by how tractable the fastest Mustang felt. "The clutch is so easy and progressive," he said. "The one in my car's not that heavy but it's like an on-off switch; and this car is comfortable enough that I could take my wife on a long drive without thinking twice about it."

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The GT500's interior has been well configured for aggressive driving, but it also has some luxurious touches. Unlike previous Mustangs, you sit nice and low in a deeply-contoured bucket seat, and the steering wheel points at you, instead of the left-side door. It and the driver's seat have a wide range of adjustment, meaning - sightlines aside - it's easy to find a comfortable driving position. Both the steering wheel and shift knob are unique to the GT500, and have a nice meaty feel in your hands; they have special red stitching to distinguish them from the regular Mustang. The ribbed seats have larger bolsters and an embossed cobra logo, and the dashboard has a leather top. The standard Shaker 500 stereo sounds terrific; "it's hardly worth filling up a third of the trunk for the 1,000-watt upgrade," Le Bret said.

Changes to the GT500's exterior are more numerous and obvious than the changes to its interior. The deeper front spoiler, sill extensions, and rear bits have been well-integrated, giving the GT500 a cohesive overall look, but one that certainly turned a lot of heads. Wherever I stopped, enthusiasts would seem to congregate, whipping out their camera phones and posing with the car. One guy working a car wash in an underground parking lot called over one of his Mustang-driving buddies from a local bank; a mailman on King street took ten minutes out of his rounds to pore over every aspect of the car.

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What's interesting here is that the GT500's aerodynamic additions are functional as well as attractive: the black front splitter and chunky rear spoiler combine to reduce lift to zero, and also help offset the extra drag generated by the larger tires; the bulging hood has heat extractors for the engine that also help reduce lift. Subtly executed details include the big, shiny exhaust pipes, the thin-spoke alloy wheels, and a nicely applied stripe kit with vintage-look lettering. There are some special colour options, too, with blue and white being my hands-down favourite.

There will be a GT500 convertible, of course, that benefits from all of the same improvements that the coupe version gets. It won't have the stripes down the hood and roof, but it offers the not-unattractive combination of a better suntan as well as easier access to the V8's noise. Hau Thai-Tang, director of Advanced Product Creation and SVT programs, says that Ford is also investigating a higher-performance version - a GT500R, if you will - that will essentially be a street-legal race car like the old Mustang Cobra R. "It's a matter of building a business case for it," he says, "but it's a car we would love to build."

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