Yes, you can do it. But its a strain on the memory controller to run 2 sets of memory over 1 to begin with. So you will have to probably set your timings to the higher latency. of course you can test lower timings , just don't be dissapointed with reality. Are those ratings at the same frequency. 1333 memory is usually rated like the 8 set, and sometimes the same set will be rated 9 9 9 24 at 1600.