What RAM should I buy?

Hi, I'm planning on building my first computer but I need a little bit of help. IDK what RAM I should buy! I've narrowed it down to either the Corsair Veangeance CMZ8GX3M2A1600C7R or the Dominator CMT16GX3M4X2133C9. Any other suggestions are welcome.

The main issue I'm having is understanding what speed rating my cpu and mb will be able to handle. I have my eyes set on the ASUS Crosshair V Formula AM3+ 990FX, it has DDR3 2133 in its description. Is that with tweaking of the bios? The cpu I'm getting is the AMD Phenom II X6 1100T BE.

Here is my future build so far:
Cooler Master HAF X
AMD Phenom II X6 1100T BE
ASUS Crosshair V Formula AM3+ 990FX
PSU undecided (recommendations?)
Graphics undecided
RAM undecided
64bit Windows 7

Thanks in advance!