If you're interested in a grand touring coupe or convertible with a heaping helping of luxury, the 2015 BMW 6 Series should definitely be on your shopping list. Whether you're on a long road trip or just your daily commute, the 6 Series treats you to strong performance, an absorbent ride and a rich interior with modern technological features.

What stands out first about the 2015 BMW 6 Series is its polished powertrain portfolio. The standard turbocharged inline-6 engine punches well above its 300-horsepower rating, while the turbocharged V8 pumps out an explosive 445 hp. Either way, the 6 Series can get you moving in a hurry, particularly with the eight-speed automatic transmission's newly standard launch-control feature. The six-cylinder also returns impressive fuel economy, yielding 25 mpg on the combined driving cycle per EPA estimates.

Beyond what's under the hood, the 2015 6 Series has several virtues worth noting. The interior makes the lofty price tag seem wholly justified, featuring top-quality materials, advanced technology and a curvaceous dashboard that's more stylish than that of the related 5 Series sedan. We also like how the convertible's glass rear window raises and lowers independently, providing ventilation with the top up and serving as a wind deflector with the top down. Drawbacks include a tight backseat (though that's not unusual in this class), a somewhat bulky feel on tight roads and steering that's less communicative than BMW's traditional norm.

All in all, though, the 2015 BMW 6 Series stacks up very well against its competitors. The 2015 Porsche 911 is a sportier alternative that comes in numerous configurations, but it can't match the 6 Series' supple ride. A well-rounded rival is the 2015 Mercedes-Benz E-Class, which comes as either a coupe or a convertible and provides a more usable backseat. The two-seat 2015 Mercedes-Benz SL-Class competes on price with higher-end 6 Series models, and it offers retractable-hardtop versatility. There's also the 2015 Maserati GranTurismo if you want something more rare. When you're shopping for a luxury grand touring car, there's a lot to consider, but the BMW 6 series is a great option that we highly recommend.

The four-passenger 2015 BMW 6 Series is available in 640i and 650i trim levels. Both can be specified as a coupe or soft-top convertible. The convertibles have a power soft top and sun-reflective leather upholstery, but otherwise they generally share the features of their coupe counterparts.

Standard equipment on the 640i includes 18-inch wheels, adaptive xenon headlights, LED foglights, adaptive suspension dampers, front and rear parking sensors, heated auto-dimming and power-folding mirrors, automatic wipers, a large tilt-only sunroof (coupe only), keyless entry and ignition, heated six-way power front seats (with four-way lumbar adjustments), driver memory functions, leather upholstery, a power tilt-and-telescoping steering wheel, dual-zone automatic climate control and a rearview camera.

Standard infotainment features include a digital instrument panel, Bluetooth phone and audio connectivity, the iDrive interface with a 10.2-inch display and a touchpad-enhanced controller, a navigation system and a nine-speaker sound system with a CD player, USB connectivity and satellite and HD radio.

The 650i adds 19-inch wheels, a sport exhaust system, a 16-speaker Harman Kardon surround-sound audio system, 16-way power front seats (with memory settings for both) and upgraded leather upholstery.

The optional Driver Assistance Plus package adds side- and surround-view cameras, blind-spot monitoring, lane-departure warning and speed-limit information. The Executive package adds the 16-way front seats and Harman Kardon audio system (640i models), power-closing doors, ventilated front seats, ceramic-trimmed knobs, a head-up display, a power rear sunshade (coupes only) and extended leather trim (650i models).

The Cold Weather package includes a heated steering wheel and a trunk pass-through ski bag. The Lighting package includes LED headlights and automatic high-beam control. The Individual Composition package includes dark exterior trim, a faux-suede headliner and your choice of various wheel designs and wood inlays, as well as premium leather upholstery in a number of color schemes (optionally with a color-matched headliner).

The M Sport package includes unique 19-inch wheels, dark exterior trim, an aerodynamic body kit, a sport steering wheel and a faux-suede headliner. The M Sport Edition package includes those features plus the contents of the Lighting and Executive packages.

Some of the above items are also available as stand-alone options.

Additional options include variable-ratio steering and an automated parallel-parking system (both for rear-wheel-drive models only), active roll stabilization, 20-inch wheels, an infrared night vision display with pedestrian detection, adaptive cruise control with a forward collision mitigation system and a 16-speaker Bang & Olufsen surround-sound audio system.

Rear-wheel drive and an eight-speed automatic transmission with paddle shifters and launch control are standard on all 2015 6 Series models, and the xDrive all-wheel-drive system is optional.

The 2015 BMW 640i is powered by a turbocharged 3.0-liter inline-6 that produces 315 hp and 332 pound-feet of torque. Thanks in part to an automatic stop-start system that shuts down the engine when stopped to save fuel, the EPA rates the 640i coupe at 25 mpg combined (21 city/32 highway) and the 640i convertible at 24 mpg combined (20 city/31 highway). With all-wheel drive, the EPA pegs both body styles at 23 mpg combined (20 city/29 highway).

The 2015 BMW 650i is powered by a turbo 4.4-liter V8 generating 445 hp and 480 lb-ft of torque. The EPA rates the 650i coupe and convertible at 20 mpg combined (17 city/25 highway), while the 650i xDrive coupe checks in at 19 mpg combined (16 city/25 highway), and the 650 xDrive convertible also returns 19 mpg combined (16 city/24 highway).

BMW estimates that a rear-drive 640i will go from zero to 60 mph in 5.3 seconds and a rear-drive 650i will do it in 4.5.

Standard safety equipment on the 2015 6 Series includes antilock disc 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 the BMW Assist emergency communications system (providing automatic crash notification and on-demand roadside assistance) and BMW Remote Services (stolen vehicle recovery and remote door unlocking). Pop-up roll bars come standard on the convertible.

Optional safety equipment includes lane-departure and blind-spot warning systems, side- and surround-view cameras and a night vision display. Bundled with the adaptive cruise control option is a forward collision mitigation system with automatic braking capability.

In Edmunds brake testing, the 650i coupe stopped from 60 mph in 109 feet and the convertible in 111 feet. Both results are about average for this class of car with summer tires.

While the 2015 BMW 6 Series is understandably not as sharp and agile as BMW's smaller and sportier models, its massive grip and composed nature should meet most drivers' expectations. The steering is reasonably precise, although it doesn't provide much in the way of feedback. This detail won't even register with most drivers, but if you've owned a BMW before, you might find the current 6 Series less engaging as a result. In any case, ride comfort is excellent, and the 6 Series remains quiet and composed at virtually any speed. The 650i's passing power is simply stunning, though the 640i is no slouch.

The interior of the 2015 BMW 6 Series is just as you'd expect it to be: furnished with top-shelf materials in a close-fitting, cockpit-style environment. If you like to spread out, however, the prominent center console might feel a bit confining. The iDrive electronics interface has a straightforward menu structure, crisp graphics and quick processing times, which helps minimize the amount of time you spend looking away from the road. Still, we still recommend that new owners sit down and familiarize themselves with iDrive before hitting the road, as it takes practice to navigate between its many functions while the car's in motion.

The 6 Series is great at accommodating two passengers up front, especially with the sublime 16-way seats that come standard on the 650i. The rear seat is too small for most adults, however. Trunk space measures 13 cubic feet for the coupe and a still impressive 12.3 cubic feet in the convertible (10.6 with the top down), and both cars have a pass-through to accommodate longer items.

The convertible's heated rear window retracts independently of the soft top, doubling as a wind deflector when the top is dropped. The heat-reflective seats are another neat feature in the convertible, and they work remarkably well.