The first DDR5 memory modules will have a frequency of 4800MHz and word has been going around for some time now that the new memory will have far greater room for voltage adjustment, which may result in better overclocking. Part of the reason here is that DDR5 has on-board voltage conversion, this task is no longer handled by the motherboard, which reduces voltage wear and noise generation.
Netac received samples of the Micron IFA45 Z9ZSB DDR5 memory and sees a path to 10,000MHz. Of course, it's unlikely these modules will be offered anytime soon. It will likely take quite some time until DDR5 is mature enough to see that kind of frequencies.
Netac currently offers a few DDR4 memory products but they are claiming to offer gaming-grade DDR5 memory with speeds beyond 10,000 MHz. It will be interesting to see Netac achieve this as DDR5's native speeds will 4800 MHz and to go to 10,000 MHz means to offer twice the speeds. It's not impossible since DDR4 memory started at 2133 MHz and we have seen several manufacturers offering kits that are rated at up to DDR4-5333 MHz that can further be pushed beyond DDR4-6000 MHz with some overclocking expertise.