Zen 2 IMC can do DDR4-5000, but it's rather pointless, because it requires un-coupled mode with IFCLK != UCLK (since IFCLK cannot be pushed to more than ~1.9 GHz, and even that is not stable on many CPUs), which adds so much latency that you _need_ DDR4-5000+ to approach the performance of DDR4-3800 with IFCLK = UCLK.