Car and Driver states the following regarding the PDK:
"For this test, we scrutinized the bestselling version of the Boxster S, which means the model equipped with the Porsche Doppelkupplungsgetriebe, a.k.a. the $3200 dual-clutch PDK automatic. It’s the quickest production 2013 Boxster money can buy, turning in a 4.2-second sprint to 60, 0.2 quicker than the manual car—quicker, even, than the base 911 with its fancy seven-speed manual. It comes by its quickness a couple of ways: Our car had the optional $2370 Sport Chrono Package and launch-control setup, which simply storms away more quickly—it’s like side-stepping the clutch in a manual car at 5000–6000 rpm—and more consistently. Then there are the PDK’s hyper-quick, Don-Knotts-on-Red-Bull shifts themselves."
So it's quicker, we knew that, but what is also interesting is the curb weight figure. The PDK weighs 3139 pounds whereas Car and Driver measured the manual at 3070. So, a penalty of 69 pounds for the PDK. The quick shifting makes up for the difference in weight.
The Boxster is getting pretty quick and when equipped with the PDK just about on par with a E92 M3. This bodes well for the Cayman which should easily be capable of mid 12's in Cayman S PDK form.