What packet rate should a gigabit card keep?

Question

linux

Need information what number of packets per second should keep a server with a gigabit card and 100 Mbps channel.
The problem is that during a distributed SYN-FLOOD attack on port 80, already at 20000pps, plugs begin to connect to the entire server (at this moment we look at the internal network from another interface)
Network card: Broadcom NetXtreme II BCM5716 1000Base-T
Channel: 100 Mbps
Axis: CentOS 6.5
All basic tuning (sysctl, backlog) done.

Answer 1

the problem is not in the card's bandwidth, but in the fact that the application is not able to digest such a stream of garbage.
...Mitigate DDoS attacks TCP SYN Flood. Cloud test...