Hi Lisha,
Very late, but just got an answer....
SAP EP on a single node(server), supports only 200 to 300 users concurrent portal users by default(the exact number depends on the hardware platform). We can scale the system with additional nodes to support more users(load balancing with additional Application Servers)
In order to test the maximum capacity(Concurrent Users) SAP Supports use of Mercury LoadRunner to execute a predefined load test in the course of conducting the Go-Live check for SAP EP.
Thanks,
Arun