I am also searching for tires and have decided on the Bridgestone Pole Positions. A great resource for tires is tirerack.com. Try the link below, then you can get reviews from everyone with a Boxster about how they liked each tire. It's a little confusing to find that - but enter you car in their search engine and it will give you loads of info.
http://www.tirerack.com/tires/surveyresults/surveydisplay.jsp?type=MP