Overclocker "Toppc" from MSI was able to crank a single stick of DDR4 memory to a world record 4,351 MHz at the International CES 2015 competition. Toppc paired the Kingston Predator DDR4 DIMM with an Intel Haswell-E Core i7-5960X processor and a MSI X99S Xpower AC motherboard. After disabling all but one CPU core and adding in copious amounts of liquid nitrogen, the 4GB memory module was overclocked to 4,351 MHz which was measured using CPU-Z (CPU-Z Validation) and verified with an oscilloscope (shown in the embedded video below).
This overclock is quite impressive even if it is not something you can run at home especially for DDR4 which is designed to use less power than DDR3. Out of the box the DIMMs are rated at up to 3,333 MHz which means they achieved an impressive 30.54% overclock (an increase of 1,018 MHz).
This kind of overclock will only result in marginal performance gains (at best) in everyday applications, but is still cool to see. Also, it surely won't hurt benchmark runs!