And it’s back. The BMW M6 took a two-year vacation and returns to the fray in a new incarnation. Now in its third generation, the most performance-focused versions of a 6 Series (this side of an Alpina or similar) debuts in the United States first as a 2012 model-year convertible. That takes place this June. The coupe version will be a 2013 model and is due later in the summer. Powering both cars is the twin-turbo 4.4-liter V8 we know and love from other machines in BMW’s stable. In this application, it makes 560 hp and 500 lb-ft of torque. That’s 10 percent more ponies and 30 percent more twist than its predecessor (powered by a 5.0-liter V10). BMW also claims an improvement in fuel efficiency to the tune of 30 percent. The coupe can zip from zero to 60 mph in 4.2 seconds; the soft-top takes another tenth. The transmission is a seven-speed, multi-mode, dual-clutch affair with paddle shifters and there’s an Active M electronic limited-slip differential. The chassis has been tuned on the Nürburgring and the car offers the option of carbon-ceramic brake discs as well as loads of other driver-centric goodies.