If you plan on playing the game at the native resolution of the LCD (the 1920x1080) then I would go and buy the GX280. The 260 can handle resolutions like 1280x800 and 1440x900 but if you want to play at that res and have everything turned up your going to need the extra power the 280 has. And a single 280 will run with the power supply you have as long as you have a spare pcie power connector.
everyone i have asked to help me wants me to give them money before they can even tell me what i need. when i try to play the game i get some prompt telling me my video specs aint up to par. i have an hp pavilion a434n. its at least 6 yrs old. when i ask my local tech what i need, he wants me to send my computer in to him. i can replace/install a board myself. i just have no idea what board to install. and when i ask someone at a retail joint they just wanna sell me the most expensive one they have whether it will work or not. i live over an hour from the nearest retail place. i dont want to make several trips. cryptic support is no help at all. the third day of trial period was when i first tried to play. my error generated a 'ticket' to send to cryptic. it was over 6 million. i dont thik i will be hearing from them in 15 min like the instrucions say.