I would say 400 watts too. 350 watts is adequate as well, but it's better to give a little more room for expansion in case you want to add SLi expansion or other things to make your PC faster and better. But yea, it will play all the games you mentioned with those specs. We have similar specs too and I'm playing those games with no problems at all. No lag of any sort.
*Fact: Microsoft Window's Blue Screen of Death vs Computerforums.org's White Screen of Death. Which is worse?