I'm slightly confused. You have 16GB of RAM now, and you are looking at 8GB of RAM that you in all likely-hood won't be able to run at it's rated frequencies because all of your RAM runs at the same timings, and the RAM you have now most likely won't run at DDR3 2133 timings.
What exactly are you trying to do?
If you're trying to add more RAM, get some DDR3 1600 at the same timings as what you currently have. If you're trying to replace what you have now, why? Going from 16GB DDR3 1600 to 8GB DDR3 2133 makes no sense. It's at best a side-grade, and really not even that. But unless you have very specific reason for adding more than 16GB RAM, I don't see what you're trying to accomplish here.
So long story short I bought some bad memory in attempt to get 2x8gb memory from amazon. They sold me crap memory and wrongly labeled it. It was sent as 1600mhz on description but it runs and is a pc3 1600 800MHZ not a pc3 12800. SCAM! So as of right now I'm running at 800mhz max :s. My other reason to get a 4x4 is because I have another computer that could use this memory later in another year when I replace its mobo. I don't need 32GB total in my comp and I don't know if I ever will unless it is really needed I would get 32GB but don't have the money. If 2x8GB is better to get for a 32GB please tell me cuz everywhere I look people say its only useful for video editing and so forth which isn't what I do.
And i think I see what you mean about the 1600 v. 2133 so a Sandy Bridge can't do a 2133? Saw that on toms forum.
"On Sandy Bridge systems, overclocking the CPU is completely independent of RAM speed. It doesn't overclock like AMD CPUs or other Intel CPUs. You can use 1333 RAM with a fully-overclocked 2500K if you want." - Leaps-from-Shadows