On a rational basis alone, the 2016 BMW 6 Series Gran Coupe is difficult to appreciate. After all, the 5 Series sedan, which the 6 Series Gran Coupe is related to, offers essentially the same powertrains and features in a more affordable, yet roomier package. But what price style? There's no denying that BMW's "four-door coupe" has a lot more visual impact than your garden-variety luxury sedan. That's what defines this niche segment, and in that regard the 6 Series Gran Coupe is certainly among the best of its breed.

If there's a knock against the Gran Coupe relative to its peers, it's that BMW wants you to pay extra, even by the segment's lofty standards. The 6 Series Gran Coupe's base prices in both 640i and 650i trim run thousands more than rivals from Audi and Mercedes. It would be one thing if the Gran Coupe were simply a superior product, but it's not -- these cars are neck-and-neck. Real-world pricing will vary, of course, but in terms of MSRPs, the BMW seems a little out of line.

Suppose you're willing to pay a premium, though, or you simply find a great deal. Cost aside, the 6 Series Gran Coupe is a highly satisfying automobile. Both available engines are gems, with the inline-6 offering attractive fuel economy and the V8 delivering awe-inspiring acceleration. The Gran Coupe looks and feels sportier than a 5 Series, yet its backseat is far more livable than that of the two-door 6 Series coupe. For the right shopper, it's a perfect blend of both worlds.

Consider, though, that the Audi A7 is cheaper than the 640i Gran Coupe and can be outfitted with a remarkably efficient and powerful diesel engine; similarly, the V8-powered Audi S7 also undercuts the 650i Gran Coupe on price. From Mercedes, the CLS-Class comes with six- or eight-cylinder power and offers value that's comparable to the Audi siblings. It's easy to see the appeal of the 2016 BMW 6 Series Gran Coupe once you take a closer look, but we still urge you to check out the competition before you decide.

The 2016 BMW 6 Series Gran Coupe is a midsize luxury sport sedan with coupelike styling. It's available in two primary trim levels: 640i and 650i. The former has the six-cylinder engine, while the latter gets the V8. Versions with "xDrive" in their name come standard with all-wheel drive.

Standard on the 640i Gran Coupe are 18-inch wheels, adaptive sport-tuned suspension dampers, adaptive LED headlights with automatic high beams, LED foglights, automatic wipers, front and rear parking sensors, a rearview camera, power-folding and auto-dimming mirrors, keyless ignition and entry, a tilt-only sunroof, dual-zone automatic climate control, heated eight-way power front seats (with four-way lumbar adjustment), driver memory settings, leather upholstery, a power tilt-and-telescoping steering wheel and an auto-dimming rearview mirror. Electronics features include Bluetooth phone and audio connectivity, a navigation system, voice controls, the iDrive electronics interface with an integrated touchpad on the controller, smartphone app integration, and a nine-speaker sound system with a CD player, HD and satellite radio, a USB port and an auxiliary audio jack.

The 650i adds 19-inch wheels, 16-way power "multicontour" seats (with passenger memory settings and adjustable side bolsters and thigh support), upgraded leather upholstery, a 16-speaker Harman Kardon premium sound system and BMW concierge services.

There are several optional packages available on both models. The Cold Weather package provides heated rear seats and a heated steering wheel. The Driver Assistance Plus package features front-side and top-view cameras, speed-limit information and BMW's "Active Driving Assistant," which bundles a blind-spot warning system, low-speed frontal collision mitigation (with pedestrian detection), lane-departure warning system and a frontal collision warning system.

The Executive package adds power-closing doors, a head-up display, four-zone climate control and ventilated front seats. The 640i's version of this package includes the multicontour seats, Harman Kardon stereo and concierge services, while the 650i's version adds a power rear sunshade, manual rear window shades and ceramic-trimmed controls. These items are available as individual options on the 640i.

The M Sport package includes unique 19- or 20-inch wheels, an aero body kit, a sport steering wheel, a simulated-suede headliner and a higher top speed limiter. There's also an M Sport Edition package that roughly combines the M Sport package and the Executive package. The BMW Individual Composition package lets you special-order leather and wood trim hues, while the Black Accent package equips the Gran Coupe with gloss-black exterior trim and a two-tone extended leather interior.

Individual options include some of the above items plus adaptive suspension stabilizer bars (known as Adaptive Drive), enhanced "Integral Active Steering" with rear-wheel steer (not available on xDrive models), a night-vision camera, adaptive cruise control, active front seats, automated parallel parking assist and a 16-speaker Bang & Olufsen surround-sound audio system.

Powering the 2016 BMW 640i Gran Coupe is a turbocharged 3.0-liter inline six-cylinder engine that makes 315 horsepower and 330 pound-feet of torque. Fuel economy for the rear-wheel-drive 640i is 24 mpg combined (20 city/31 highway). The all-wheel-drive 640i xDrive is just marginally thirstier at 23 mpg combined (20 city/29 highway). In Edmunds performance testing, a rear-drive 640i Gran Coupe zipped from zero to 60 mph in 5.7 seconds, which is average for this class of car.

The 650i Gran Coupe packs a turbocharged 4.4-liter V8 that generates 445 hp and 480 lb-ft of torque. Fuel economy drops to 20 mpg combined (17 city/25 highway) for the rear-drive 650i and 19 mpg combined (15 city/24 highway) for the 650i xDrive. In Edmunds testing, a rear-drive 650i Gran Coupe hit 60 mph in 5.2 seconds. Although that's adequate for a V8-powered midsize luxury sedan, the Audi S7 and Mercedes-Benz CLS550 are significantly quicker.

It's worth noting, however, that we observed a slight software-related launch delay in our acceleration tests. In other words, the sprint to 60 mph doesn't fully represent the engine's potential. In the quarter-mile sprint, the BMW closes the gap, indicating plentiful real-world acceleration.

Standard safety equipment includes antilock brakes with advanced standby and drying features, traction and stability control, front-seat side airbags, front knee airbags and active front head restraints. Also standard are front and rear parking sensors, a rearview camera and the BMW Assist emergency communications system, which provides automatic crash notification, remote unlocking, stolen vehicle recovery and on-demand roadside assistance.

The optional Driver Assistance Plus package features front-side and top-view cameras, speed-limit information and BMW's "Active Driving Assistant," which bundles a blind-spot warning system, low-speed collision prevention (with pedestrian detection), lane-departure warning system and a frontal collision warning system.

In Edmunds brake testing, a 640i Gran Coupe with summer tires came to a stop from 60 mph in 110 feet, while a similarly outfitted 650i stopped in 114 feet. These are short distances compared to typical vehicles, but unremarkable for this segment.

Its acceleration numbers may be nothing special, but the 2016 BMW 640i Gran Coupe certainly feels quick in everyday driving. The turbocharged inline-6 picks up steam rapidly as the revs climb, and the automatic transmission is on point as well, providing quick and timely downshifts. Similarly, the 650i's laggardly sprint to 60 mph doesn't tell the whole story, as noted above. When you open the throttle to merge or pass, the ultra-refined V8 unleashes a seemingly endless flow of thrust, moving the big sedan down the road with intoxicating authority.

Every 6 Series Gran Coupe has that unflappable Germanic feel at high speeds, yet somehow manages to feel smaller than it really is when you drive it around turns. All the while, the ride quality is firm, yet suitably luxurious for a car of this price and level of prestige. That said, we're not so enthusiastic about the optional active steering and stabilizer bars. Specifically, the steering lacks the company's trademark road feel, while the sophisticated stabilizer bars are actually too effective, decreasing body roll to the point that you no longer have a sense of how hard you're pushing the car.

The Gran Coupe's interior is distinctly more driver-focused than that of the 5 Series sedan. Mirroring the two-door 6 Series coupe, the Gran Coupe provides wraparound controls and a prominent center tunnel, creating a cockpit-like environment. Materials quality is top-notch, while the specific trimmings are highly customizable. Depending on your preferences, the appearance of the cabin can range from richly luxurious to edgy and avant-garde.

The front seats are superbly comfortable and low to the ground, reinforcing the car's sporty character. Rear seat passengers certainly fare better than in the 6 Series coupe, but worse than in the 5 Series due to a significant reduction of headroom and the so-called "+1" center rear seating position that's really only useful for children on very short trips. That center seat has essentially zero legroom of its own, as the Gran Coupe's extended center console runs all the way to the rear seat cushion.

Like other 6 Series models, the 2016 Gran Coupe features BMW's iDrive control interface, which manages entertainment, navigation and phone functions as well as various vehicle settings. The control knob includes a touchpad that lets you draw letters and numerals with your finger on the controller's touchpad surface. Although we advise you to take some time to study the various features before you hit the road, iDrive is notable for its sharp graphics, fast processing times and logical menu structure.

Trunk capacity goes the way of rear-seat headroom in the 2016 Gran Coupe. There are just 13.0 cubic feet of total cargo capacity, and the trunk liftover is rather high. At least the rear seat has split-folding functionality and an armrest pass-through to help improve utility.