Multiple Video Card Build

Hello, I am building a machine that will be outputting to 9 different monitors for security cameras. I am trying to figure out a good amount of RAM to put in this machine. I have it at 8GB RAM right now, but feel that it is a little light. My build right now is a Dell Precision T7600 with:
(2) Intel Xeon E5-2603 1.8GHz Processors
8GB DDR3 1333 RAM
(3) AMD FirePRo V7900 Video Card
600GB SAS 10k Hard Drives in RAID 1
Win 7 Pro 64 bit

I'm having a hard time figuring out how much RAM I really need, but the machine will be displaying live and recorded video and nobody has a spec sheet anywhere, so it's sort of a guess for me.