The Boxster S shows 252 wheel horsepower stock and the Cayman S shows 256 wheel horsepower stock on the AWE-Tuning Mustang dynamometer. Porsche does tune the Cayman S slightly more aggressively than the Boxster S.
The AWE-Tuning exhaust system is just a rear section so the gains are not exactly huge. Peak output on the Boxster S rises to 256 wheel horsepower and on the Cayman S it rises to 261 wheel horsepower. Gains of 4 and 5 wheel horsepower respectively.
This is mostly a modification for exhaust sound quality but it is nice to see the dyno results for the Boxster S and Cayman S.