Any unit on this page would be a great choice. My personal choice would be the Seasonic X 850. Although I believe that XFX is the same model internally ( made by Seasonic like all XFX units ) and is cheaper. So it's probably the best value. The Corsair AX 850 is also a Seasonic X internally.
Yes, more is better than just enough. Don't make the mistake I made. I bought a nice Seasonic 620, and it works great but I will not be able to SLI 770s without changing it out for a more powerful one. Spend $120 now instead of $80+ $120 later. I wasn't initially interested in SLI, because I had a bad taste in my mouth from AMD Crossfire years ago. Now I will have to buy another power supply if and when I choose to SLI.