System requirements for coop.

Hello.

I have corei5 4570, 16Gb DDR3 and GF 460GTX, Win10Pro x64
I feel performance drop in cooperate game.

It seems it does not depend on the graphics adapter. Feel performance drop even on low settings.
And it does not metter who is server (me or my friends).

Have you any suggestions how to improve performance?

Thanks.