Performance test caps at 600 Mbit/s

[MrFastDie]

Hello,

the last days I played a little with the NGINX settings and the tcp stack to
test the best performance. I used direct connection between my testing
machine and my server using a cat5e cable.
My nginx.conf can be found at pastebin: http://pastebin.com/rRAEwvNc
My sysctl.conf also provides lot of changes: http://pastebin.com/KmPjEnHN
My /etc/security/limits.conf provides soft nofile at 1048576 and hard nofile
at the same value.

I'm not using any kind of firewall, all logs are disabled, neither the cpu
nor the ram is at it's limit, the i/o load seems fine to me too, but the
internet speed caps round about 600 Mbit/s. This test was made with 2000
connections per time and a 1MB file.

The server contains an Intel(R) Pentium(R) Dual  CPU  E2220  @ 2.40GHz and
has 3.5G of Ram.
My local computer contains an Intel(R) Core(TM) i7-4710HQ CPU @ 2.50GHz and
has 16G of Ram.

The limits and tcp changes were also made on my local computer.

Is there someone who can help me to deal with this problem?

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,271846,271846#msg-271846