Go to tire rack.com (eliminate space) and search to fit your vehicle. Read some reviews (there will be plenty for Boxster's...) and choose from there. Then either order and have shipped to one of their installers or go see installer directly and ask them to order. I like the latter way b/c then they also make a couple $ on tire sale along w/ install.
Otherwise, I usually like to go with black round ones. At 6,100 miles and just finishing my 4th set I seem to use them a little differently than you. As such, any addl input will not be helpful
Good luck
