Can someone recommend me a x79 for this CPU.

Just make everything though PCPartPicker to make sure everything works.

I would suggest going with a Haswell build instead of Sandy/Ivy Bridge-E. The 7990 is a very high-end card, but you'd be better-off saving the money because a higher-end CPU for gaming will make a marginal difference in performance. A 4770K, Phanteks PH-TC14PE, mid-range Z87 board, 8GB of RAM, a good 750w power supply, and the 7990 would be better.

As far as I'm aware you can run at whatever speed it's rated at - 1600 MHz is just the official RAM rating. Anything over that is unofficial - just like overclocking.

You don't need to be dropping half a grand on a motherboard.

If you're going gaming only, save money and go for a 4670k, high end AIR cooler, a quality 750w unit with gold ratings and haswell ready etc etc and then either 2x 7970 or a single 7990. I would personally get 2x 7970 for cooling reasons, but that's up to you. It'll most likely cost more getting 2 individual cards.