Ram Issue When Overclocking Cpu

HI

So let me present my rig :

i7 950

8 Go of RAM instead of 12Go ( 2*2Go died )

MSI x 58 Pro E

GTX 580MSI Twin frozr II

Thanks to my motherboard, I can OC hardware wise with the OC switch. By doing I can go up to 4.0GHz instead of the stock 3.07 GHZ

the only issue that I have , is that only 4 or even 2 Go of  Ram are reconized instead of 8Go, how is that possible ??

then when I switch back to the stock clock ( 3.07Ghz) I have my 8 Go, Crazy isn't it or is that normal ??

I can overclock with the bios but as i'm not skilly enough doing a such thing, I'm scared that i'll do the wrong thing.

Any idea ?

thanks

CMB