I too have this issue running and I7 2600K 8G RAM and an Asus 560ti and it is infuriating. I should be deciding what my machine is capable of here not ARMA. If I wanted to know what arma thinks I would press the AUTODETECT button.
This issue has actually made me not want to play the game and the issue was not as bad when I first bought it.
Please fix this issue Bohemia, Please. I will be getting a gtx 780 soon and if it still does it with that I will be seriously annoyed.