I have 3570k and 7850 OC 2GB with 8GB RAM, and can play dayz maxed with smooth fps (I have high res textures). Only had to slightly lower some settings to remove fps drop in fast combat. With 7870 you should easily be able to play at maxed.
I have post processing disabled, dont know how much fps it would drop, but naturally when playing dayz you should turn it off. Because if its turned on you cant see shit if you try to look at long distant.