Because the Pontiac Aztek did so well for General Motors, German automaker BMW felt compelled to present its impression of that most puzzling of vehicular amalgams, the fastback-bodied sport-utility vehicle. Meet Munich's production X6, which debuts in the official-unofficial sense ahead of next month's North American International Auto Show in Detroit. Due in U.S. showrooms roundabout the middle of next year, the X6 — BMW calls it a "Sports Activity Coupé," despite its four doors, to differentiate it from the old-fashioned X5 — will debut in two forms: The xDrive35i features a twin-turbo 3.0-liter in-line six with 300 horsepower, and the top-drawer xDrive50i packs a new, 4.4-liter V-8 with direct-injection and twin turbochargers, good for 400 horsepower and 450 pound-feet of torque. Four-wheel drive is, of course, standard, complete with BMW's Dynamic Performance Control, which can shunt power to the wheel or wheels with traction. No word yet on production plans for the X6 ActiveHybrid Concept from this year's Frankfurt Show.