While I've tested Catalina, I don't recommend it, yet. Wait until 10.15.3 is released to make sure all the major bugs are fixed and the 5700 drivers are "matured".
Also, be aware that Catalina changes the disk structure and security for non Apple approved kexts/drivers. (That's one of the reasons that MultiBeast hasn't been released yet.) If you upgrade to Catalina before MultiBeast for Catalina is release (real soon now), put your kexts/drivers in ...Clover/kexts/other.
The Sapphire RX 580 drivers in Mojave are mature. So, I'm not thinking about getting a 5700 series graphic card until next year. My RX 580's serve me well.