performance issus, please help???

[w3elf]

I am using Autobench to test the nginx server performance. The numbers i
generated above are when the response times are still very low. After
than, more requests per second starts to error out. 

IE:
4x 512 mb apache server, 1 nginx server( 2048 mb) :700 requests per
second
4x 2048 mb apache server, 1 nginx server( 2048 mb) :700 requests per
second

the range of testing was from 500 -1000 requests per second. the
response times and network IO increased steadily until it hit 700, then
response times increase dramatically and network IO stayed flat at that
point.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,214412,214454#msg-214454