maybe it's furmark? it could be giving a false reading. it could also be your overclocking program. try MSI afterburner for OCing and try MSI kombuster to stress your card. but like amuffin said, it just could be the chip, like a manufacturer cap or something.
I think you're both right, I checked it in MSI afterburner and it's reading the same thing, 999mhz but that's enough for me anyways, just wanted to know if this is normal.
Thanks for your help.