a 2x2 is more suited for a 150w bulb, not 1200w of juice. If you put 2 600w in a 2x2x2 your box will be as hot as the sun.
Can you get 400g from one plant? Yes. One plant per 600w.
Big Bud, Chronic all yield nice. Hell, any plant will yield nice if you have one of em under a 600.