Porsche is ready to launch its all-new 911, code-named 991, at the Frankfurt Motor Show. That means that the former model, the 997, will immediately be rendered obsolete, right?Well, yes and no. The production version will, of course, be replaced by the 991. But Porsche has decided to keep the world’s most popular car for customer racers all around the world, the 911 GT3 Cup, based on the 997 until at least 2013.