911 Turbo S
There was a 993 Turbo S. And a 996 Turbo S, too. But so far, we have not seen a Porsche 997 Turbo S. Reason? Dunno, though we imagine that a more powerful turbo would step on the toes (among other parts) of the hard rocking GT2. Especially as the fastest of all 911s "only" makes 40 more horsepower than the plain ol' Turbo. And besides, 520 horses is probably pushing pretty hard against the edge of the performance-to-reliability ratio that OEMs have to worry about (unlike, say, tuners).