Thats a pretty nice rig there and I would think that the games you are talking about are not going to be anywhere near the capabilities of the system.
I have a similar setup of a 940 on an asus m3a78 board with 6gb of ddr2, a 550w psu, and a 4770 graphics card, i run both of those games at 1680x1050 at near max settings.
You mention the word lag? I assume your playing online multi-player? could this problem be due to internet connectivity? have your tried rebooting your modem, router, and computer....etc... have you run a speedtest on your connection? what type of connection do you have?