Hellfire: I read news about hardware/computers for 8 years, also I have built many computers and I am just saying taht your processor is not able to bring enough data to those graphics card your are willing to buy. Simple idea..you have processor which is costing about 75dollars and you want to buy graphics card for 300dollars...not good idea for well-balanced system.
One month ago, I have assembled computer with Core i7 920 and radeon HD 5850...you want to buy as strong graphics card as HD 5850 is, but your CPU is 5 times worse than Core i7.
Simply buy HD 6850 or GTX 460...I think these cards can fit your system well
Anything stronger will be wasting money for nothing