You could try lowering some of the minor settings and scrape a few more fps out of it.
It's odd though cause my desktop runs Arma 3 pretty good and it's not as good of a set up as yours.
Have you tried running programs that monitor cpu gpu and mobo temps while your playing?
If somethings heating up after extended periods of play it may cause issues. Although from my experience the few tims I've seen it, you generally end up with a BSoD.