1600 is the suggested data rate for Intel Haswell CPUs, it's their 'limit', Some non-K Haswell CPUs can easily handle 1866 and even 2133 . It generally will OC the MC (memory controller) a bit to do so, the K model CPUs can handle even higher data rates - I run 2666 on one of mine and 2800 DRAM on the other (in sig), generally at worse it may take a slight CPU OC and possibly a little extra voltage to the MC (all of which is perfectly safe)