The 3.2 wins, especially the '03 - '04 flavor.
I think it's been proven for the most part that most of the "bolt on's" provide little to no real world performance benefit on the Boxster motors. Porsche has done a REALLY good job of wringing as much power out of these motors as possible and that's proven out by the lack of effect most bolt on's have. Of course a full blown, none street legal header, exhaust, intake and chip version of the 2.7 might put down numbers at or above a stock 3.2 but when you look at the "area under the torque curve" you'll see the '03 - '04 3.2 simply provides more power in more places.
Now, take the 3.2 and do the same things to it and you're approaching the Carrera performance envelope
Of course this is all IMHO and YMMV
