I have a Corsair HX850 with no regrets.
As for why such a big psu, well its a good question, but a general rule, 2x what you need for max efficiency and low stress on the power supply.
My HX 850 was on sale anyway
to that end, my system has trouble pulling over 350 watts(but i do not have 2 video cards either.), so maybe i went a bit too far.