BIG-IP 6900 Series number of open conection

Dears

 

i am using BIG-IP 6900 LTM in ISP with 100K users to load balance http traffic to four caches, i am only using simple configuration that use wild card virtual server with round robin balance , the CPU load is 15% with 45% memory , my internet connection is around 400Mbps , the problem is that after using F5 the internet link usage is dropped to 250Mbps

 

so am i using the wrong hardware , do i need to upgrade to higher end , i noticed the number of open connection in peak hour is around 800K connection ,so can 6900 hardware handle all this connections without performance degradation??