The FX-60 from 2006 I think was the last AMD CPU that held this crown. 2.6Ghz and it beat Intel's top chip at 3.5Ghz. The only thing on the market with higher single threaded performance was their own FX-57 which was single core with a slightly higher clock speed.
I still have my old FX-60 in an antistatic clamshell. I just could never bring myself to get rid of it, I loved that processor so much. That and XPx64 held me for a very long time.
https://www.anandtech.com/show/1920