i was stuck in the same boat as you, and no, 2gb will be the same as 1gb noise wise, but the 6970 graphics card dosnt need 2gb, its a waste of money and memory, it works just like ram in your imac, only that its for the graphics. Its called vram, and it depends on what your going to be doing. IF your running multiple monitors, 2gb will help, if your running games, video's etc, 1gb is best.