The letter R is a dangerous one when used in a vehicle trim designation.

It’s commonly associated with a high-performance model (or a car made to look like one); take Volvo’s R-Design line, Acura’s old Integra Type-R as examples. Same deal with the word “spec,” used by Nissan (Sentra Spec-V) and Acura (on its short-lived TL A-Spec). The use of such a designation often yields what I’ll politely call mixed results. Some such-named cars turn out great, while others are total duds that do little more than give the carmaker an excuse to charge more for an aging product.

So, here’s Hyundai, a company not known for performance cars or luxury cars, with the Genesis R-Spec, a new performance-oriented version of one of its most luxurious models. What could possibly go wrong?

A little background on the Genesis. It was named North American Car of the Year shortly after its introduction in 2009, and then spawned a Genesis coupe variant based on the same chassis, but styled and marketed as a distinct car.

With the even larger Equus joining the Hyundai lineup in 2011, the Genesis was booted out of the flagship spot to play second fiddle in the brand’s portfolio. As if to placate this former top-dog, Hyundai gives the Genesis a few new toys for 2012, including direct fuel injection and more power for the 3.8-litre V6 engine (333 hp (up from 290) and 291 lb-ft of torque), a new 5.0-litre V8 engine with a ground-pounding 429 hp (an increase of 44 compared to the 4.6-litre engine it replaces). And, because it’s apparently never possible to have too many gears, there’s a brand-new eight-speed automatic transmission, in place of a six-speed.

Aside from its impressive power output, the new V8 is also signficant because it’s only available in that new R-Spec trim. This is a fantastic engine that moves the car effortlessly no matter how fast you want to go. And this car is fast: it scooted from zero to 100 km/h in 5.8 seconds in performance testing at the 2012 Automobile Journalists Association of Canada Car of the Year awards, and Car and Driver measured a zero to 60 mph (96 km/h) time of 5.1 seconds. What’s even more impressive is how this motor produces the power to move this 1,884-kg sedan so quickly. It’s unbelievably smooth, and makes beautifully refined sounds no matter what you ask of it. If I had one wish for this engine, it’s that the throttle was less hair-triggered. It’s a bit of an on-off situation: you’re either accelerating (albeit gently) with light pressure on the throttle, or you’re off the throttle and slowing down.

The engine’s smoothness should be a positive thing, and it would if the nearly-silent powertrain didn’t render the car virtually devoid of any personality. This car has lots of ‘go,’ but lacks the mechanical ‘show’ that any car wearing a badge like R-Spec should put on, both for the driver and those outside the car.

But the biggest disconnect in my mind was between the strong-but-serene powertrain and the kidney-killing ride. There’s not much grace in how this car handles rough roads; it tosses its occupants around like a hang glider in a hurricane, while the steering twitches with bump steer over every crack in the pavement. I expect this kind of stuff in, say, a Mini Cooper, but not in a big luxo-sedan. If there’s a plus, it’s that the big 20-inch wheels don’t transmit much noise into the cabin, even over rough pavement, a mean feat for a car with such a stiff ride.

Perhaps the payoff is the R-Spec’s handling, which is impressive for a two-ton-plus car that doesn’t also happen to be a Porsche Panamera. But sharp turn-in and handling are betrayed by electric-hydraulic power assisted steering that communicates nothing about the road beneath the tires to the driver’s hands. The steering is also very heavy at low speeds and makes the car a chore to pilot through narrow city streets and tight parking lots. A sporty car needs a meatier steering wheel rim than this, too.

If the R-Spec does anything right, it’s highway cruising. On smooth asphalt, the car is a dream at freeway speeds: quiet, stable and planted – a very comfortable long-distance vehicle, indeed.

That holds true for the seats, which are comfortable all around but as it seems with many luxury cars, big and small, headroom is at a premium. You won’t lack for legroom, though, or cargo space: the trunk is vast, and is limited only by the lack of a folding rear seat, common to other Genesis sedan models, and indeed to most big luxury sedans. Asian carmakers seem to figure that if people can afford their cars, they can afford to have someone else bring big stuff home from Ikea for them. The driver gets three-stage heating and cooling functions for their seat, but the front passenger makes do with heat only. The rear seats are heated, too.

Stereo operation relies almost entirely on the central control knob in the console, while also handles commands for other high-tech funtions in the car. It’s not a terrible interface, but the similar BMW, Audi and Benz systems provide more redundant controls on the dash, which I prefer. Hyundai also has a strange predilection for dictating that iPods must be connected using their propriety connector (included with the car); a standard USB cable won’t work.

A basic Genesis with the 3.8-litre V6 comes with a starting price tag of $39,999, which continues to be a steal for the amount of luxury this big sedan provides. The R-Spec, being top of the pops, is significantly more dear, at $53,499, but that difference is reasonable considering you get an extra (nearly) 100 horsepower and loads more luxury kit. Not to mention that you won’t find this combination of speed and luxury for 53 grand in any of the Genesis’ competition.

If the plain-Jane Genesis was ambitious car for Hyundai in 2009, this performance-bent R-Spec version was an even more audiacious move. However, for every thing this speedy Q-ship does right, there’s something else that doesn’t quite fit the formula. Where a regular Genesis is a solid luxury car effort at a really good price, the R-Spec feels like it was rushed into production. And while there’s nothing horribly wrong with it, it just doesn’t feel like it earned that letter R.