I had 4 Gb (2x2) of crucial ballisitx cl7 on my gigabyte mobo with an athlon 245 (2.9ghz) all standard settings no overclocking.
I have just installed another 2 x 2Gb crucial ballistix cl7 to give 8 Gb total. both 1333mhz
Now my windows experience value was 5.9 for memory, I just re-ran it and its leaped to 7.2! how come such a big leap? when there has been no speed increases.
although my desktop graphics looks a lowly 4.4!!!!! nothing to do with the ram, just thought i'd say. next is 5.4 so this value is quite low so my overall WEV is 4.4. it is using on-board graphics so I would expect it. I'm not a gamer so not bothered.
But you now have double the ammount of sticks in your system so it can access the memory faster because it has more of it to access. It can access the other 2 sticks at the same time as the other 2 sticks. They are all clocked the same as the original 2 sticks but there are now more of them to access.