I just put in 2 more gigs of ram into my pc. I had 2x512 of ddr2 5400 and I added 2 more gigs 1x2 of ddr2 6400 ram. I know they will only run at 667 MHZ but then I decided to just put in the 2 ddr2 6400 and they still only run at 667 not 800mhz. I used CPU-z and it said that the 5400 was running at 333mhz. I need an explination?