Have you actually tried running the memory in 3600MHz + 1800MHz FCLK? The CPU (memory controller) should be the deciding factor of how fast you can run the memory speed and infinity fabric.
Ryzen 5000 should easily be able to do 3600/1800MHz, possibly even Ryzen 3000. The 2000 series may have trouble reaching 3200/1600MHz depending on the memory setup and chip quality.