How can that be? Though the Porsche is more powerful, the Infiniti has a better power to weight ratio. The 315-horsepower Infiniti FX45 weighs about 600 pounds less than the 340-horsepower Porsche Cayenne S. Do the math. (Actually, we'll do it for you: The 4,949-lb. Porsche uses 1 hp per 14.5 lbs.; the 4300-lb. Infiniti has 1 hp per 13.6 lbs.) Infiniti claims the FX45 is quicker than the other hot-rod SUVs, namely the Mercedes M55 AMG and the BMW X5 4.6is.

At the same time, the Infiniti models cost less than their German counterparts.

These performance and pricing advantages come partly by making a conscious decision that Infiniti's new luxury sport-utilities would not be designed to go off-roading. Therefore, the FX45 frame could be lighter, lightening the load for the Infiniti V8.

The weight advantage was just a starting point, however. Infiniti added enormous 20-inch wheels and tires and racecar-sized brakes. Infiniti's goal was to make the FX45 as fun to drive as a sports car. It achieves this by compromising in ride comfort, space and rock-climbing ability. The end result is a car-based crossover SUV that's exciting to drive on sports car roads and full of character, but has a stiff suspension and ride, a tight cockpit, and flamboyant styling.

Squeezing into the cockpit and bouncing along a bumpy snow-belt backroad in the FX45 will appeal only to confirmed sports car enthusiasts. Infiniti expects to sell just 30,000 per year, while BMW last year sold about 43,000 X5s.

The suspension reflects Infiniti's decision not to make the FX an off-roader: Generally off-road ability is enhanced with long-travel and compliant suspension tuning, but that same ability compromises handling on winding roads. FX is tuned for those winding roads, and despite its tall 7.6-inches of ground clearance, it has no skid plates or underside armor. FX is based on the same Front-Mid engine platform used for the Nissan 350Z sports car and Infiniti G35. Thicker frame members make FX strong enough to handle the extra weight of the bigger four-door wagon body.

Marketing played a role in the FX's pure pavement identity: Infiniti doesn't believe anyone who spends up to $50,000 for a crossover SUV will risk scratching it in the dirt.