For those who have doubts that 2133MHz RAM does not make any improvements in gaming and overall PC performance:
http://www.anandtech.com/show/4503/sandy-bridge-memory-scaling-choosing-the-best-ddr3/1
"It's only when you get down to DDR3-1333 that you see a minor performance penalty. The sweet spot appears to be at DDR3-1600, where you will see a minor performance increase over DDR3-1333 with only a slight increase in cost. The performance increase gained by going up to DDR3-1866 or DDR3-2133 isn't nearly as pronounced."
Also from the Crysis and Metro 2033 benchmarks, there wasn't any significant improvement in FPS?