One of the weak points of AMD's Ryzen is that the platform doesn't really support high DDR4 memory frequencies. Intel-based systems support much higher DDR4 overclocking but it seems this will change with the introduction of the Zen 2-based Ryzen 3000 series.
TechPowerUp heard from Ryzen memory guru Yuri "1usmus" Bubliy that AMD seems to have a made a lot of progress.
Zen 2 BIOS settings reveal memory frequency options of up to DDR4-5000, which is a huge step up versus the previous generation. The settings also reveal a new 1/2 divider mode, which will run Infinity Fabric at half the actual DRAM clock:
The DRAM clock is still linked to the Infinity Fabric (IF) clock domain, which means at DDR4-5000, Infinity Fabric would tick at 5000 MHz DDR, too. Since that rate is out of reach for IF, AMD has decided to add a new 1/2 divider mode for their on-chip bus. When enabled, it will run Infinity Fabric at half the DRAM actual clock (eg: 1250 MHz for DDR4-5000).