I currently have a 7950 3gb. I play at 1440p and I am in need of a second card in order to max out my frame rates. Its impossible to find a used 7950 at a reasonable price. I bought mine new for 310$ a year ago and all the used ones I see are for 450 plus. When the r9 280 non x comes out can I use it in crossfire with the 7950 or should I sell my 7950 and buy a r9 280x- r9 290 non x?