With a full decade behind it now, it’s official: The Cadillac CTS is a winner. But now it’s time for a second test for GM’s premier brand. The 2013 Cadillac ATS is about to confront some of the auto industry’s heavyweights on their own turf in the high-performance, mid-size sports sedan arena. The ATS specs include rear-wheel drive (AWD optional) with a choice of three gas engines, including a 2.5-liter naturally aspirated four cylinder unit, a 2.0-liter Turbo with 270 ponies and a 3.6-liter V6. Throw in MacPherson struts, a ZF electric power assisted steering rack, Brembo brakes, and an aluminum hood, and it’s clear the BMW 3-Series will have some looking over the shoulder to do.