The fastest of NEMIX's three RDIMM speed grades runs at 6400, rated CL52 — the third timing bin in the same server lineup alongside the CL40 (4800) and CL46 (5600) kits, with no other CAS option sold at this speed.
This 4×16GB configuration is 64GB, rated 6400 MT/s CL52. Capacity again spans 16GB up to a 128GB four-module kit, the same range covered at the other two speeds in NEMIX's RDIMM lineup, so it's the module count rather than the total that changes most between listings.
Like the rest of that lineup, this is registered ECC RDIMM DDR5 for server boards, not a substitute for unbuffered consumer memory in a standard desktop system.