I do want to OC so it's looking like I might need to RMA -- unless the G.SKILLS Ripjaws are awesome OC'ers (any comments on that)? Anyway, what makes these two identical-looking modules different? Is the memory tested in the lab and subsquently graded "1333" or "1666"?
You did not mention the specifications of the RAM. The memory is rated for certain values, if you would like to use them together, you should try settings they can both support. It can be difficult to achieve good results with two separate kits, so it is best to use only a single 32GB kit.