Another thing you may want to consider is testing the ram with memtest. http://www.memtest86.com/download.html
and checking your psu's. you have 4 computers on a network at the same time playing BF3? what is your network speed. where are you located and where is the server you are playing on located? if you are in asia playing on a US server with a low bandwidth, it could be you are experiencing lag due to the long delay in communications.