Arma III/Arma II DayZ

The engine they use for the ARMA games is very CPU intensive (but can use more than 2 cores if available). As for GPU, if you want to run ARMA II at highest, I wouldn't go any lower than a 560Ti or AMD equivalent and a intel I5 High end CPU (or AMD equivalent)...which would give you a stable about 40+FPS.

As for ARMA III, they haven't really worked out the optimal system for it.

If you're building it yourself, I would say your PC would cost about 1000$ to build a proper ARMA III very high setting rig.

If I was building a ARMA III system, I'd go with something like...

CPU: I5-2500K OCed
GPU: 560Ti SLI or Single 660Ti or higher (if you end up with a good deal)
RAM: 4, 6, or 8 GIG or DDR3 (again, depending on deals)
Mobo: MSI makes very good motherboard for overclockers...check 'em out.

The rest is up to you...