The register in question is called the FCLK (or 'f-clock'), which controls some of the cross-frequency compensation mechanisms between the ring interconnect of the CPU, the System Agent, and the PEG (PCI Express Graphics). The FCLK, or Fabric Clock, is the frequency at which the IF, or Infinity Fabric, operates at. For FCLK adjustment, we're only interested in MCLK, or the actual memory clock speed – 1,800MHz. TL;DW: Going for high frequency is a waste of time. One aspect we didn't cover yet is memory and FCLK overclocking on a Ryzen 9 3900X.