i probally don't have to say this, but stock for stock the S2000 and the RX-8 are very simalar:
RX-8:
Curb Weight: 3029 lbs.
HP: 238 @8500
Torque: 159 @5500
S2000:
Curb Weight: 2810 lbs
HP: 240 @8300
Torque: 153 @7500
In the basic catagoires they are quite simalar, really the only question to ask is if you what to sacrafice 2 extra seets for 200 lbs.