Yeah I figured as much with ARMA. I was actually more just hoping I could actually play it within that budget constraint.
My main focus is on DCS and being able to run that very well. I use to fly and a friend just introduced me to DCS and its about the closest thing that I have ever played to the real thing, but now I am forced to upgrade my pc to be able to play it like I would like.
You should actually be pretty well off. That PSU is excellent, and if you already have a monitor and keyboard, you should be able to get a good build for $500 - $600. I'm not great at picking out parts, so I'll leave that to someone else, but you should be able to max out Arma II and DCS for $500 - $600.