Given the multi-die configuration of EPYC, best performance is achieved by ensuring that at least one DIMM per memory channel is populated. This ensures that the full memory bandwidth of all 8 memory controllers is leveraged and the NUMA domains are fully balanced. In the specific example referenced the 128G implementation that would provide best performance is 8 x 16G DIMMs vs 2 x 64G DIMMs. This of course assumes the memory speeds and types (1R, 2R, LR, etc) are equivalent.