arma 3 seems to run very nicely on intel for me, however a brief google search shows that some people have fps problems no matter which cpu they are using, a friend of mine has the fx-8350 and seems happy running dayz on it so.... either cpu will serve you well
As an Arma 3 player. I would HIGHLY recommend the i5 4670k at this point. Arma 3 is horribly optimized and hardly uses 4 cores even with start up commands. Since Intel has much faster single core performance the i5 will be significantly faster than the 6300 or 8320.