Question, do you get good frame rates in Arma II by itself?
Alot of times mods are coded in such a way that they use a whole lot more (CPU) processing power than a game by itself, however they don't have significantly higher GPU requirements than the base game (it's the same graphics engine, but if they have lots more enemies,effects, higher textures, etc it still adds to the GPU load); you should start out by figuring out if you can run Arma smoothly and at what settings. Try those out in DayZ, if it's not smooth, turn them down some, if you hit the minimum and it's still not smooth it's the processor (if you managed to run arma smoothly that is).
If you can't run Arma smoothly, then you are probably getting bottlenecked by the GPU, but both the CPU and GPU could be the problem.