I've been looking at videos of these settings or very similar ones and from what I've seen you should be fine up to 1080p. ArmA 3 has released system requirements on the systemrequirements lab website.
Just Google "Can You Run it?"
And I'm wondering the same thing....Your RAM is half of mine. Unless you mistyped it?
His RAM is 1333 you double that given figure hence DDR being Double Data Rate
You should run BF3 at low settings at 1080p (if you want high framerates) if you can deal with lower framerates then go medium.
Well I've been playing around with the specs I can play at ultra around 25-30 fps but it does randomly drop somehow I use to play it on the earlier missions and heavy intensive graphic missions on ultra just fine but now it goes around 10-20 fps so I run it at high around 60+fps some times it drops down to 45 but it usually keeps 60+