cmd51

So I recently purchased Combined Forces from Steam and i installed Day-z the mod, I have been getting such fps drops and my pc is pretty good. My fps is around 17 - 27 its unplayable i don't know maybe I set the wrong settings but every thing seems to be fine when I play in the Armoury or editor (ARMA II) i get the standard 40 - 60 fps just Day-z. My specs are AMD X4 965 3,4 GPU: 7870 OC Sapphire 2GB 4GB Ram PS. I can run BF3 on High 1080P Please HELP !! :((