OP if your budget is really 4000 dollars there is no reason you shouldnt get two, three, and maybe four 7970's. if you go that route a 7970 used about 225 watts of power. so you would need a 1200-1300 watt psu max
No, if you want the fastest, buy two 780 ti.
Radeons still have crossfire issues, and the 780 ti is faster anyway.
And for a PSU go seasonic they are the best in the business and offer a 7 year warranty on the good stuff.
Ps I am going to cry if you build a 3930k system with the liquid cooling and don't overclock it at least a little....
Samsung 840 pro is a great drive to consider, that's what I would go for!