BSX class is 2900 with driver (my car weighs 2710 empty)
BSR class is 2650 with driver (empty car is around 2470)
Boxster Spec Racing Official Website
It just depends on how far you want to go. Stock muffler, A/C system, stereo, carpeting all add weight. Eric523 has a great BSR build thread on Renntrack. His car is to-the-max and he really knows how to drive it.
Guess who just got a boxter?