I've researched some ram and I find that there isn't a real difference i would notice between 1600mhz between 2133mhz. I've looked at the G.Skill Sniper series at 2133mhz 16gb 4x4 at 9,11,10,28 and the Corsair Dominators at 1600mhz 16gb 4x4 at 7,8,8,24. Which would be the best? I do alot of hardcore gaming with all the settings as high as they go, as well as do a lot of overclocking overall!
If you have any other suggestions i'll be running an I7 3770k and the gpu would be the new gtx 780 once it's released probably sometime April if I had to a take a quess. This is all for preparation.
One poster stated he couldn't run higher than 1600 with all four ram slots populated, so don't be surprised if you can't run them much higher than that. It has to do with latency and stability; getting all four to run in sync. You might run faster with a 2 x 8 gb kit leaving two slots empty.