Congrats on your Boxster. I'm guessing in Japan it's not a common car.
Check out the information on Tirerack's website about load ratings (the 88 and 92) and other good tire info.
Unless you see some cold temps I'd recommend summer tires for your Boxster. They are in general going to offer better dry and wet grip then all seasons.
By the way - you may want to take the other post down since its identical to this one.
Happy tire shopping.
Tire Tech Information - How to Read Speed Rating, Load Index & Service Descriptions