That's the tricky thing with computer parts. Sure that graphics card will do you well with Arma 3, if the rest of your system is up to scratch. But then there's always better options out there, at the trade of more money. If you don't have the funds right now for something along the lines of a 1070 or even 1080 then the choice is yours: buy a cheaper card risking it being outdated for anything new coming out, or invest a little more to then be more future proof.