Ignore the AMD fan boy pushing inferior gaming processors.http://www.tomshardware.com/reviews/fx-8350-core-i7-3770k-gaming-bottleneck,3407.html
For gaming, the I5-3570K is as fast as the I7_3770K, and faster than the AMD_whatever
You always want to get the most powerful graphics processor you can because the games get more and more demanding year by year. Far Cry 3 brings a 680 to its knees even with a 1920 X 1080 display.
With $400 you can get either a 7970 or 670. Again, which one to get is a massive debate. I'd suggest one or the other. Either one will max out your games and should last for a few years.http://www.newegg.com/Product/Product.aspx?Item=N82E16814103201
This seems to be the best rated 7970 card.http://www.newegg.com/Product/Product.aspx?Item=N82E16814162109
This seems to be about the best rated 670. Personally, I'd go for this one.