FMS3 videochat capacity

Hi,
I'm trying find out some capacity test for videochat. It will be enough know numbers of clients on conrete PC configuration. Can anyone tell me some numbers of streams and users? Or when I will have overall 1000 users, when each user is "downloading" 4 stream and from that 500 users are "uploading" camera. What configuration can handle it? It's only example. It will be enough know any numbers of users/configuration. Thanks a lot!
Leoš