I just bought a used 6600XT off Ebay for under $300 and it works great. The 5700XT I got first randomly hard crashed my the system, apparently it's a known hardware issue so avoid those.
Otherwise I have the same CPU as you; I'm on KDE Neon. Just be sure your 500W is enough, I think it should be but you're getting close. be quiet is a quality brand though, so it should handle narrow margins just fine. I have a 600W IIRC. A GPU with a selectable Eco/Quiet mode via BIOS switch could give you more flexibility there too.