Starting at the least-powerful, the X6 xDrive35i uses a turbocharged inline six-cylinder engine to pump out 300 horsepower and 23 mpg average. All-wheel drive is standard in all X6s, as is an eight-speed transmission--except for the X6 M.
Moving up to the V-8 range, the x6 xDrive50i generates 400 horsepower from a 4.4-liter twin-turbo V-8. Despite the larger power output, the xDrive50i only suffers a 3 mpg combined gas mileage penalty compared to the xDrive35i.
The wild and insanely fast X6 M uses the same displacement as the xDrive50i, but extracts a massive 555 horsepower from a more highly-tuned, upgraded engine. Due to the huge power output, the X6 M uses a more robust six-speed automatic transmission.
All X6s handle well, their somewhat carlike looks betraying their equally car-like on-road handling. Body roll is present, though much less so in the X6 M, and the eight-speed transmission in non-M models delivers smooth, quick shifts in either automatic or paddle-shifted manual modes.
Acceleration is brisk, steering is direct and natural though sometimes vague in feel, and ride quality doesn't suffer to deliver these qualities--except in the X6 M. The X6 M is more capable than you'd believe possible in an SUV; enabling M Dynamic Mode takes the electronic safeguards to new performance heights while still throwing out a safety line when needed.
Off-road, the non-M X6s are also surprisingly able to traverse moderate terrain, but the expeditions should be left to more focused off-roaders.