Good point I forgot to mention my power supply.
It's a Corsair 600W CX Builder Series 80 Plus Bronze
http://www.ebuyer.com/269259-corsair-600w-cx-series-v2-psu-6x-sata-2x-pci-e-cmpsu-600cxv2uk
or
http://www.corsair.com/builder-series-cx600.html


I'm also mining scrypt so i'm guessing the 3GB cards would be better than the 2GB ones?