I could wrap up this review in one sentence: “The 650i Gran Coupe is a 550i with less rear headroom.” But that wouldn’t really do the car justice. There is more in the mix here – I promise.

Rather than embracing the Gran Coupe as a sleek 5 series, it is more apt to figure it a stretched 6 series with four doors. In truth, both cars are built upon the same base chassis, but there are significant tweaks and changes – enough to make each car distinct; just drive a 550i against a 650i to feel the difference – trust me, it’s vast.

The 650i Gran Coupe, then, is a classy 6 that seats 4. Well, technically 5 if you count seat belts, but no one with this much money would have friends willing to sit in economy and straddle a rear console – at least not for long.

Unfortunately, if you have tall friends the Gran coupe will become a four-door two-seater. Tested in the age-old trick of ‘sitting behind oneself’ I had my hair rubbing the ceiling and my neck unimpressed in the rear quarters. I stand six-foot two-inches, admittedly on the tall side of average, but I must level this criticism against the Gran Coupe: that purely in the name of fashion, the car contains less function. This of all trespasses stands in heresy of age-old BMW design philosophy, where form follows function – or drive an Audi.

This single greatest flaw in the 650i Gran Coupe – and it’s only a flaw if you expect tall-ish adults to join you for a trip – sets it apart from all other BMW sedans in the lineup. If your kids are not about to hit a growth spurt and you seldom carry adult passengers, feel free to pull the trigger and indulge in what is probably BMW’s most beautiful interior, ever.

So sleek, so sexy, so rich and lush is the Gran Coupe’s cabin that it makes the 7 and 5 series seem obsolete. Talk about model cannibalism. If a plush interior is purely what you’re after, I can’t imagine settling on any other BMW. This interior is swanky in an upscale Audi kind of way – and that’s a massive compliment.

Rich leathers meet up with contrasting colors, hides, metals and plastics in organic, flowing lines to deliver an optical treat. Reach out and your fingers will be rewarded with lush tactile sensations from every surface. Press buttons, spin knobs and the precision of finely crafted jewelry and timepieces will meet your hand. I cannot overstate the beauty and elegance of this interior. It’s worth of a trip to your local BMW dealer just to sit in it and check it out. Finagle a test drive if you can.

Add in BMW’s wide array of advanced comfort, entertainment and safety technologies and the Gran Coupe begins to feel like a luxury Starship Enterprise. Every toy and trinket is on option from an infrared camera to a heads up display, lane departure warning systems and blind spot monitoring systems, a kicking Bang & Olufsen must-have sound system to a panoramic sunroof. You could play for hours in this car without driving an inch.

But when you do finally get down to driving duties, the Gran Coupe will continue to impress. BMW has recently bumped the output from its twin-turbo 4.4 liter V8 to a healthy 445 hp and 480 lb-ft of torque.  These figures are deep into serious sports car territory. Consider the rock solid chassis, perfect weight distribution and rear wheel drive, and it becomes clear that the Gran Coupe is a driver’s car.

I was afforded the opportunity to spank the BMW 650i Gran Coupe down a few Californian back roads, and it did not let me down. The chassis is indeed stiff and well balanced with moderate under-steer dialed in by the legal team. The steering has decent feel and excellent precision, pointing the nose exactly where your eyes and hands guide it.

ZF’s brilliant 8-speed automatic is on duty to shift cogs, and it performs best when left to its own devices in sport mode. The torque is endless and there are too many gears to fiddle with, so intervening with the transmission proved superfluous. It shifts when and where it should and after a hard drive in sport mode, it will carry revs all the way to redline and upshift under hard braking to keep the revs up. The transmission-engine package works very well together and suits the car.

The brakes were a touch small for a ‘sports car’ weighing 4,200 lbs and sustained brake fade – though they did hold up well unless provoked for longer stints of fun. A track day would not treat these brakes kindly, but if you don’t see a race circuit in your Gran Coupe’s future (and the vast majority of owners won’t) – don’t sweat this detail.

My single greatest complaint against the Gran Coupe’s dynamics boils down to its tires. The 650i Gran Coupe is considerably under-tired and could stand to use wider, stickier OEM rubber, particularly at the front with a less staggered arrangement. This alone would mitigate a great deal of the understeer on hand and offer much better grip through corners – the chassis is otherwise ready for any road or track. The good news is: this is a very simple and inexpensive (and fun) upgrade for any owner to undertake after purchase. I’m pretty sure BMW Performance might even have a few suggestions for you.

For those that long for a track-day Gran Coupe – you’ll have to wait until summer of 2013 when the new M6 Gran Coupe is launched. It will be worth the wait. All others less motorsport inclined would do well to ensure rear passengers are under 6 feet and then sign on the dotted line. Ahh… that interior.

Pricing starts at $86,500 USD and jumps rapidly from there depending on options. Over 30 K of add-ons can quickly bring the price over 100 grand, and for that money you are nipping at the heals of an Alpina B7 – a car worthy of bedroom poster space and adult salivation spells.

In some way the Gran Coupe reminds us of BMW’s X6. The Gran Coupe is to the 5 series what the X6 is to the X5: a less practical version of the same basic vehicle. But – and it’s a huge but – if you value cuff links over comfort – the Gran Coupe is your car.