With that mobo, go with the 1600. It will give you more options, more settings to tweak, when overclocking compared to the 1333.
But then again, if overclocking is the goal, then you might want to check out the G.SKILL Ripjaws Series 8GB (2 x 4GB) DDR3 2000. What you lose in latency you gain in sheer speed, plus even more overclocking combinations between the RAM and CPU.
Whichever RAM you choose will work well with that mobo, so....good luck!