The normal Boxster is shit slow! (and cheaper than most expect - only around 30-35k for old models I think) I remember a Best Motoring race where it was up against GTR, EVO, NSX, RX-7, etc and got left half a lap behind.
In the end the guy driving's like, "Well, I like the interior".
Boxster S is not bad, and I would seriously buy it over the Cayman S. Hmm.... convertible version cheaper than hardtop - not a hard decision. I just don't like the lack of widespread aftermarket tuning options available, especially for entry level porsches.