I'm not sure - 8v8 on freon is about right. 31 players was.....funny occasionally
UT2004 is single-threaded so in theory I suppose we could have 32 players on each of the 12 threads... I'm not sure how the network traffic would be.
I still have a hankering for a faster processor - just so that 32 player vCTF/ONS would remain smooth for longer.