This is not very easy to answer. DayZ or Arma in general lacks of optimization. You can try to go to "Can you run it" and check. You should get a very high "outcome". Basically, if you were to play singleplayer DayZ you could easily run the game on high with no problems but on a stable server with, let's say 30 players, you should try going for medium setting, and you would probably hit those 60 fps