Kingston recently revealed a new lineup of HyperX DDR4 modules that clock up to 5333 MHz, which would make them among the fastest commercially available DDR4 stick on the market. The new HyperX parts will, unsurprisingly, be expensive, with a 16GB set to cost over US$1200.
https://www.notebookcheck.net/Blazing-fast-Kingston-Predator-DDR4-memory-clocks-at-5333-MHz-out-of-the-box-but-could-cost-over-US-1200.538615.0.html