Even the basic DDR5 specification is faster than all but the best DDR4 kits, at around 4,800MHz, but that may not be anywhere close to its full potential. Netac, a Chinese memory manufacturer, is aiming much, much higher with its experimental 'ultra high frequency' kits. How does a DDR5-10000 kit sound to you?
Netac is aiming for a 10,000MHz (effective) memory kit with DDR5 memory (via ITHome, El Chapuzas Informatico), although it's got a long way to go yet. The company says it just received its first batch of DDR5 DRAM from Micron, a batch of MT60B2G8HB-48B ES:A RAM. That part number appears to correspond to DRAM DDR5 16Gb kits.
Micron's DDR5 DRAM is officially rated between 3200–6400MT/s, between 1.1 and 1.8V, and is available with up to 64Gb per chip. That's potentially a whole lot of memory per DIMM.
Samsung has managed to stuff 512GB of DDR5 DRAM onto a single stick of RAM. That's SSD-sized system memory—makes even 32GB of DDR4 look paltry by comparison.
Netac will need to push Micron's quite a distance to tip it over 10,000 MT/s (10,000MHz effective), which will likely necessitate some very loose timings and high voltages to achieve. It's certainly not impossible, however. DDR4 is able to reach speeds more than double its 'stock' speed nowadays.
Memory kit manufacturers will all be looking to push DDR5 memory to the limit with every new memory kit, and I suspect the race will be on to hit a DDR5-10000 kit just for the acclaim. Memory manufacturers—namely Micron, Samsung, and SK Hynix—will also want to be the chip of choice for high-performance RAM kits, such as Samsung's infamous B-die DDR4, and will undoubtedly offer more performant chips as time goes on.
For gaming workloads, you'll want tighter timings and a solid relationship between memory speed and memory controller, which is found on your CPU. None of today's chips from AMD or Intel will be suitable, either. AMD's first DDR5 compatible chip will arrive with the Zen 4 architecture, expected to arrive in 2022, and Intel has confirmed both DDR5 and DDR4 memory support will come onboard its Intel Alder Lake processors later this year.