I just upgraded my computer with another R9 270 because it wasn't quite cutting it in Fallout. Tested it with Unigine Valley before and after adding the second card and got about 80% higher score. Play fallout and there's no noticeable improvement, but there are periods of horrible chunky lag like 3-4fps. Most of the info I've found is before the FA4 1.3 update in February and apparently not very useful. All driver's up to date and the game is up to date via Steam. So, does anyone have Crossfire working with Fallout4?