for 2 quad gigabit cards the example is this

vi /etc/modules.conf

or

vi /etc/modprobe.conf

depending on your version of kernel

add

options e1000 RxDescriptors=4096,4096,4096,4096,4096,4096,4096,4096 TxDescriptors=4096,4096,4096,4096,4096,4096,4096,4096 RxIntDelay=1024