The longer it takes for DDR5 memory to grab a foothold in the market (none of AMD's or Intel's consumer platforms support the next-gen memory standard...yet), the higher overclockers will continue to push DDR4 RAM. Now the record to beat is a hair over 7GHz.
That is incredibly fast for DDR4 memory. It was just over a year ago when I naively wondered if overclockers would break the 6GHz barrier on DDR4, and sure enough, some did with a kit of G.Skill memory. Now 14 months later, bragging rights belong to Micron and its Crucial Ballistix Max memory.
Micron got a huge assist from an overclocker in China who goes by "baby-j," who validated their achievement at CPU-Z and HWBOT. They set the record with a single Crucial Ballistix Max DDR4-4000 memory module, hitting 7,004.2MHz. That represents a 75 percent overclock over what is already a fast frequency.
The record overclock was also achieved using MSI's MEG B550 Unify-X motherboard and a Ryzen 5 Pro 4650G processor. And as you might expect, the RAM and CPU were bathed in liquid nitrogen. So in other words, this is not something you are going to duplicate at home on a whim (or with air cooling), nor does it have any real-world application.
Nevertheless, in the realm of record overclocks, baby-j deserves a tip of the hat for going further than anyone else ever has with DDR4 memory. At least for now. We won't see any consumer DDR5 platforms this year, but I wouldn't be surprised if this record gets broken before 2021 rolls around.
That said, DDR5 is in mass production as memory makers prepare for future chipsets. The first kits will run at speeds from 4,800-5,600MHz. That's not 7GHz, but they also will not require any exotic cooling, just good old fashioned heatspreaders and good airflow.