The automotive press spends plenty of time pondering the purpose of performance-tuned SUVs like the BMW X5 M and the Jeep Grand Cherokee SRT8. Critics question the rationality of a performance vehicle that's unnecessarily tall and heavy; they dispute the sacrifice of off-road ability in an SUV tuned to run quick quarter mile times. After all, these hot rod SUVs may be quick on pavement, but with wide, slick tires, most would find themselves stuck should they venture into the winter weather or onto the trails.

So what's the point?

Well, the six SUVs here - Mercedes-Benz ML63 AMG, Infiniti FX50, Porsche Cayenne Turbo, Range Rover Sport Supercharged, Jeep Grand Cherokee SRT8 and BMW X5 M - are decidedly special. The premium cost of entry and limited utility means that most buyers will prefer their cheaper and less extreme sibling models, making them rare. They are all blisteringly quick, despite being large and heavy machines. They give drivers that tall and commanding view of the road, yet they bring sports car-like agility. They sound mean, announcing their arrival wherever they go. They're SUVs for people who can afford a Jeep Wrangler, too, should they choose to hit the trails.

Here they are, in all their nonsensical glory.

Mercedes-Benz ML63 AMG
The all-new for 2012 M-Class Mercedes SUV is immediately available in ML63 guise, tuned by AMG, the company's in-house performance group. The new body is all flared and squatty in the AMG, with wide intakes up front and four pipes rumbling out back. The previous model's 6.2-liter V8 is out, replaced by this third-generation's twin-turbo 5.5-liter V8, good for 518 horsepower, second only to the BMW's 555-horse output here. But at just under 5100 lbs, the Mercedes is lighter than the BMW. Like the Infiniti, the ML63 uses a 7-speed transmission. Unlike the Infiniti, base price is $95,865, so the ML63 can easily hit the hundred-thousand-dollar mark with a few options.

Infiniti FX50
Being confined to the pavement is perhaps less a stretch for the FX50 than for other vehicles here. Even in less-sporty FX35 trim, the model is not particularly intended to hit the trail. This makes the performance version a good fit for this crossover-like SUV. With a 390-horsepower 5-liter V8, the FX50 is the least powerful vehicle here, but it's also the lightest at just over 4500 lbs. Plus, the price is right. Here, only the Grand Cherokee SRT8 undercuts its $60,245 starting price. The Infiniti is arguably the more sophisticated machine, with elegant curves and lots of high-tech features. Buyers in this price range who favor subtlety will likely prefer the FX50 to the more flamboyant SRT8.

Porsche Cayenne Turbo
Are you serious? The Cayenne Turbo certainly is. It's not the most powerful vehicle here, nor is it the lightest. But a bit of arithmetic proves that each of the Cayenne's 500 horsepower must push just 9.57 lbs of SUV down the road - that's the best power-to-weight ratio in this group. The 4.8-liter twin-turbo V8 sends power through an 8-speed transmission, the only such gearbox here. Buy the Cayenne Turbo for outstanding performance from one of the world's great sports car makers, not for practicality. Cargo space is tight, but hot rod SUV shoppers won't likely notice. What cannot go unnoticed is the $107,100 base price, a $10,000 premium over the next most expensive vehicle here.

Range Rover Sport Supercharged
If the Infiniti is a more elegant choice compared with the Jeep, the Range Rover Sport Supercharged is the choice that makes the higher-priced vehicles here look pedestrian. Indeed, the high-performance SUV from the esteemed British marque makes a statement thanks to its heritage, but the secret of the Sport Supercharged is that it's actually a bargain compared with the pricey German muscle trucks. And it doesn't skimp on power. A 510-horsepower 5-liter V8 propels the $75,245 Rover through a 6-speed automatic. Don't expect performance on par with the 500-pony Porsche, though. The Range Rover Sport Supercharged weighs in over 5800 lbs. Only the Infiniti has a power-to-weight ratio weaker than the Range Rover's.

Jeep Grand Cherokee SRT8
Even if you find giant hood scoops to be garish, it's hard not to be impressed with the value proposition of the Jeep Grand Cherokee SRT8. Starting at $55,295, the all-new for 2012 Jeep is the least expensive model here, yet shares much of its underpinnings with the costlier Mercedes ML, a result of the now-defunct marriage of Mercedes to Jeep's parent company, Chrysler. Under the hood though, the Grand Cherokee SRT8 is all American, with a normally-aspirated 6.4-liter Hemi V8. It delivers 470 horsepower through an automatic transmission with only five speeds - the only gearbox here with so few ratios. While the Jeep isn't the most technologically advanced vehicle, the value doesn't end with the price. The Jeep also offers good cargo space in this company, adding everyday practicality.

BMW X5 M
The "M" stands for "Motorsport," the focus of BMW's in-house performance specialists. And sporty this motor is, producing 555 horsepower, the most of any here. The BMW does it with less, too. The 4.4-liter twin-turbo V8 is the smallest displacement engine of these hot rod SUVs. At 5368 lbs, power-to-weight ratio is nearly as good as the Cayenne Turbo's. But starting around $87,000, the BMW's price undercuts the Porsche's by a significant $20,000. Practicality is not typically an important consideration in this segment, but the BMW does offer more cargo space with the second row seats folded than others here. With the rear seats up though, cargo space is least in the group. What driver of a 500-horsepower SUV needs practicality, though? In fact, should you eschew it, there's always the M version of the fastback X6, a vehicle with no discernable practicality whatsoever.

Just as critics condemn these high-performance machines as contradictions, they cannot stop talking about them. After all, these are the latest and greatest of a relatively new breed of automobile. They combine the SUV form with awesome power and equipment suitable to the world's best sports cars.

author photo

Nick Palermo is an automotive writer and lifelong car nut. He follows new and late-model used vehicles for AutoTrader.com, writes about vintage cars for Hemmings Classic Wheels and blogs on all things automotive at LivingVroom. He lives in Atlanta with his wife and twins.

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