Put simply, the BMW 650i is smooth and precise. It's easy to drive, always poised, and satisfying to drive at a brisk pace. The ride is taut but not harsh. It's easy to modulate the brakes and throttle and the steering is sharp. All the important controls work cohesively, making for a smooth driving experience.

The engine is silky smooth and tractable for easy going around town or in stop-and-go traffic. Yet you're rewarded with immediate response whenever you press down on the accelerator, and the reward is a bit more lavish for 2006. BMW has bumped displacement in the 6 Series engine from 4.4 to 4.8 liters, increasing the output to 360 horsepower and 360 pound feet of torque. The 32-valve V8 benefits from Valvetronic variable valve timing and variable lift, which allows an impressive combination of low-rev, off-the-line acceleration and free-breathing, high-rev horsepower. The V8's breathing is controlled entirely by the valves. (Technically, there is no throttle, so the pedal on the right is more accurately called an accelerator.) It's a fascinating engine for engineers and car buffs, but the bottom line is that there's loads of power throughout the rev range, so the 650i responds immediately in any situation. It's also an efficient engine, so energy is channeled into fuel-efficient power. The engine sounds great, emitting a guttural roar under hard acceleration through its nicely tuned exhaust system. Response is impressive in either the coupe or convertible, though convertible drivers enjoy those sweet engine sounds a little more intimately.

Of the three transmissions available, we recommend the six-speed automatic, unless you're a serious enthusiast, in which case we recommend the six-speed manual. We're not big fans of the SMG. The automatic is smooth around town and very responsive for spirited driving. In fact, a 650i with the automatic is nearly as quick as a well-driven 650i with the manual. As with all BMW automatics, it offers a Sport setting that moves shift points to higher revs for increased response. The Steptronic manual mode allows the driver to shift manually, imparting some of the same involvement as a manual. We found little need to shift into the manual mode, however, because the transmission always selected the right gear in automatic mode. The manual gearbox is smooth, precise and easy to shift, with easy clutch pedal effort. It's an excellent choice, unless a driver spends hours daily in stop-and-go traffic. The sequential manual gearbox, or SMG, is the essentially same transmission as the manual, but it operates the clutch electronically, eliminating the clutch pedal. Though we've enjoyed the SMG in the M3, the version in the 650i shifts too slowly and takes away some of the joy of driving this car.

The 650i offers a nice balance of ride and handling. Though taut, it doesn't beat up your passenger on rippled highways. The springs and shocks are firmer than those in the standard 5 Series sedans, and the 6 Series cars ride lower. A 650i is absolutely joyful on a winding highway, as we discovered on some mountain roads near Santa Barbara. Handling is precise, with a superb self-centering feel to the steering. The 6 can be driven very hard into tight corners, and it tracks through high-speed turns like it's on rails. The suspension is tuned to minimize undesirable behavior when braking hard, accelerating hard, or lifting off the gas while cornering. Our car was equipped with Active Steering, which is now a stand-alone option. The system improves high-speed stability and makes it easier to steer in parking lots. Some drivers don't like BMW's active steering; I'm not one of them.

Active Roll Stabilization dramatically reduces body roll (lean) when the 650i corners. As the car leans into a corner, the anti-roll bars are twisted by little hydraulic motors that counter-act the body lean, so the 650i leans very little, even in hard cornering. In addition to increasing driver confidence, the system improves handling over bumps, increases cornering capability, and improves steering response.

Drive the 650i past the limit of the tires and the Dynamic Stability Control and other active safety systems kick in, allowing the car to motor around corners with little drama. The DSC works toward keeping the car from skidding into understeer or oversteer, making it easier for the driver to maintain control. Simply aim the 650i where you want to go and it'll go there, assuming the laws of physics allow it. If it snows, press the DTC button to turn on the Dynamic Traction Control system. This system will manage engine power for you, and keep the rear tires from breaking free and spinning.

The brakes are excellent, with big, lightweight discs and calipers, and resistant to fade even after several hard stops.

Yet, for its impressive performance envelope and response, the 650i is not the least bit finicky when driven at a lazy pace. The 6 Series cars come standard with aggressive 245/45VR18 high-performance run-flat tires. The coupes and convertibles we drove were equipped with 19-inch wheels, part of the optional Sport Package, and they rode well. The main drawback is more noise over bumps or pavement joints.

The convertible is remarkably quiet with the top up, nearly as quiet as the coupe. As mentioned, the power rear windscreen can be lowered even when the top is up, though we didn't find it significantly added to air circulation. Conversely, the rear glass can be raised when the top is down to act as a wind blocker, but turbulence with the top down was minimal in any case, and raising and lowering the glass didn't seem to make a big difference. In short, this is a fun feature and we like having it, but it has no significant practical benefit. With the windows up and top down, the 650i convertible makes for great open motoring even on briskly cool days.