2 sticks of MATCHED memory will allow you to use dual channel more instead of single channel. There is a small gain in performance with dual channel. But I'm not certain you would notice it. Having twice the memory, of course, speaks for itself. Since games are still 32 bit coded, they can only access 4GB system memory. But if all you have is 4GB, Windows will be using some of that too. As will the graphics buffer.