Yes Entomb is 100% right go with 16GB kit the you can still add more RAM in the future if you need to with ease. The rest looks good, enjoy your new gaming machine! Question what monitor are you going to use?
-You want more power with your PSU especially if you do SLI and overclock, so I swapped for a EVGA G2 850W which is well regarded.
-Switched to dual channel 16GB RAM because its more convenient and its cheaper. No performance loss.
-Added a Nepton 240M CPU cooler because it'll have lower temps and is an excellent CPU cooler. Here's a LinusTechTips review of it: http://youtu.be/65-aR4o8iT4
-Switched to Enthoo Pro because its the best value full tower and you'll want the extra space with two GPUs and a radiator. Here's a review by Hardware Canucks: http://youtu.be/cBhmn21ylkc
I wouldn't recommend Razer headsets. I've heard that they produce cheap products and aren't worth the price.