YOU HAVE TO KEEP REMINDING YOURSELF while dusting switchbacks in the Austrian Alps with the new Porsche Cayman S that this is not your dream car. This is not the 911 Carrera, the car in the posters that once wallpapered your bedroom. If the 911 has always been your best friend, your trusty go-to, your touchstone and ne plus ultra in a world flooded with automotive mediocrity, then, well, you're just going to have to let that go. The Cayman is all grown up now, and your attention is about to be whipsawed. The 911, er, what? Who?
Tacking into a steep valley toward the empty ski village of Warth, 4905 feet up the slopes of Western Austria, where the landscape looks as meticulously manicured as a model-train set's, the…