Not bad specs. Try bumping your settings up higher. ARMA, if you didn't know, is a CPU intensive game. That means if you have your graphics all the way down, your CPU will be working way harder than it would be if you evened out the load between GPU/CPU. Try running standard settings. Then maybe high.
Try also toying around with the overall view distance and object distance. Also, if you go into the in-game phone and click the cog wheel app(settings) you can lower your view distance that way as well, hopefully making rendering a little easier on your PC.
Let me know what happens when you try all these.
P.S. Worst case scenario, just use GeForce Experience to optimize your game. That will hopefully help too.