I have high performance BF Goodridge g-force tires, which are great for non-autocross/racing. These where on the car when I bought it, and I have put about 14k miles on them and they still have plenty of tread, at least another 14k miles probably closer to 20k. I have used them to autocross and was fairly competitive, and I do not go easy on them around town either.
If you can sacrifice a little performance you can get tires for the Boxster that will last 35K+ miles.
http://www.bfgoodrichtires.com/overview/g-force-t-a-kdw/22.html?WT.si_n=TSV&WT.si_x=6
Porscha
Threaded Mode
