Phoronix published a review on the Overclocking The Radeon RX 580 Under Linux
A quote from the article:
Yesterday I posted the initial Radeon RX 580 Linux benchmarks while now with having more time with this "Polaris Evolved" card I've been able to try out a bit more, like the AMDGPU Linux overclocking support. Here are the ups and downs of overclocking the Radeon graphics card under Linux.Overclocking The Radeon RX 580 Under Linux @ Phoronix