PC Gamer recently got to spend some time with Arma 3 at E3, and they've answered 8 questions from their readers.
What hardware were they running it on and how smooth did it play?
Very, very smoothly. A frame counter wasn’t visible, so don’t interpret this as scientific, but I felt I was running at 50-60+ frames throughout the demo. Bohemia was running a Core i7 at 3.2 GHz and a single GTX 580. Not low-end equipment, certainly, but I wouldn’t call that exotic, either. I encountered one or two microscopic hitches while helicoptering, but the game behaved extremely well overall. There was no noticeable dip in framerate when I right-click zoomed in most situations, and gunfire/explosions had zero effect on performance. The largest mission I had probably had 20-25 enemy infantry (and an enemy vehicle) scattered across a kilometer or two, plus my six or seven-man squad.