Thanks for the reply but could you elaborate please. When I bought the rig it had two ATI 3870 cards in it, the only difference so far is one GTX 560Ti. At the moment the most watts used is 255 ( I have the PC plugged into a device that measures usage) and the PSU is rated 650 I believe.
Will another GTX 560TI really use that much more? If so what if I just change the possessor for a Q9650?