arma uses more CPU than a lot of other games because the amount of scripts, objects and AI the CPU has to recognize and execute over the course of the game.
but since you mentioned DayZ also it might be just be an issue of Arma 2 or your CPU. You can try to give your CPU a bit more juice with an overclock (since you have an excellent motherboard) just make sure to get an aftermarket cooler (you can get some really decent ones at around the 30 dollar range so it's not a bank breaker).
for Arma 2 specifically I've heard that if you turn shadows up it will make the game run smoother because the GPU will take the load, but when you turn it down your CPU will take on the burden instead and further slow down your game.
I suggest you reinstall your drivers also, wipe them clean and use AMD's catalyst suite (an annoyance as a program but honestly pretty good in terms of functionality) to install the drivers and optimize settings for games.