A slide leaked by Turkish outlet, Technopat indicates that the sweet spot for the memory speeds on the Ryzen 5000 CPUs will be 2000MHz (DDR4-4000), up from 1800MHz on the Ryzen 3000 parts.
This indicates that the Infinity Fabric and Memory Controller clocks will run in a 1:1:1 ratio with the memory till 2000MHz, after which it will be decoupled and run in a 1:1:2 ratio. Memory overclocking has a massive impact on gaming performance on Ryzen processors due to the chiplet design. The Infinity Fabric speeds directly impact the inter-core latencies which are a major contributing factor to overall performance, especially in gaming workloads.
This means that the Ryzen 5000 processors will likely get an additional performance boost in gaming when paired with DDR4-4000 memory in a dual-channel config. With Ryzen 3000, going from 3200MT/s to 3600MT/s in DC mode roughly increased your frame rate by 3-5%. Going from 3600MT/s (1800MHz) to 4000MT/s (2000MHz) should confer a larger performance boost in the same scenarios.