Well a lot of the decision has to do with what AMD CPU you're running, and the Games you want to play, and the resolution you're playing them on i.e. monitor. Also, if your current GPU is capable of Crossfire then that might be something to ponder -- to a point on the second x4 PCIe slot.
Keep in mind most expensive GPUs will be 'bottle-necked' to your CPU in comparison to a Sandy Bride.
i have phenom II x4 955 3.2ghz, I was just looking for one card, I have an older monitor the resoulution is 1440 x 900. I have 800W psu and 4g of ddr3 memory. that card you linked will that work? im fine with not running games at ultra but it would be nice, I wont see most of the benefits though because of my screen