G.Skill has claimed the world record for the fastest, overclocked DDR4 memory by boosting a single 4GB module of their Ripjaws 4 Series DDR4 RAM up to 4,255 MHz with timings of 18-18-18-63. As the modules are typically clocked at 2,400 MHz, G.Skill managed to add an extra 1,855 MHz with liquid nitrogen cooling.
The company achieved this record on an Asus Rampage V Extreme motherboard with an Intel Core i7-5960X, the highest-end consumer-grade CPU from the chip manufacturer. Although the X99 chipset and CPU support quad-channel memory, apparently running just one stick of DDR4 in a single-channel configuration is better for overclocking records.
While the feat is certainly cool, it's worth nothing that increasing the speed of your memory to such a ridiculous level probably won't improve the performance of your system by all that much. Memory performance typically isn't a bottleneck in anyone's PC: it's more likely your system is limited by CPU, GPU or storage performance.
In fact moving from DDR3 to DDR4 memory won't make a huge difference in the speed of your PC, at least initially. Memory performance is usually several years ahead of what anyone would need in their systems, and a typical stick of DDR3-1600 is more than enough for most users, especially in multi-channel setups.
However it just goes to show how fast you can make DDR4 memory go if you really push it, especially with a healthy supply of liquid nitrogen to keep it running ultra-cool.