Just a quick one, I'm building this rig at the moment and it'll have 4GB of ram... I read that's plenty enough for LTC mining but would a multi-coin switching pool like middlecoin require more ram for any reason?
Actually, RAM does become important once you start to go over a certain amount of GPUs in your rig. You may have to lower you TC to compensate.
The cgminer error you'll get could be "Error -5: Enqueueing kernel onto command queue." and one or more of your GPUs wil be disabled.
For example, 7x7950 with 8GB ram and a TC of 24000 gives me the error whereas it was working with 6x7950. Lowering TC to 22400 fixed it and had little to no effect on my hashrate.
I have no idea why that is though, as memory usage is < 2GB once cgminer does get to work.