Last year I was at a Porsche event and had the opportunity to drive the Boxster GTS, Cayman GTS and 911 Carrera back to back. The cars were evenly matched regarding power en weight. The Boxster GTS has 330 hp, the Cayman GTOS 340hp and the standard Carrera 350bp. The Carrera is slightly (25kg) heavier than the other two, offsetting the small advantage in power.
There were a couple of surprises.
Firstly, the Cayman GTS is much more hardcore than the Boxster GTS. This is partly due to the fact that the Cayman GTS we drove had the optional sports suspension; 20mm lower with no adjustable dampers. The Boxster GTS, on the other hand, was on standard adjustable dampers (PASM) and felt much more rounded and easy to exploit. The Cayman GTS (exactly the same car that I drove for my review here), is better suited for track work, though.
Secondly, the 911 Carrera felt slower than the two GTS cars, but not necessarily because it was slower, but because it was masking its speed. Looking at the speedo you realise that you are going much quicker than you think in the Carrera. On the other hand, with the Boxster and Cayman you feel like you are going faster, which adds to the fun.
The 911 is the practical proposition; it has back seats and it is very comfortable, in a GT way. The Cayman GTS, with the option of the extra sporty suspension, is probably more suited to track work and felt nervous on the Catalan mountain roads we drove. For me, on this roads, the Boxster GTS was the pick of the day.