A user on the ChipHell forums posted what appear to be base and boost clocks for the purported Ryzen 9 3900XT, Ryzen 7 3800XT, and Ryzen 5 3600XT. The CPU, which clock up to 4.8 GHz seem to be a short-term counter to Comet Lake S while AMD preps Ryzen 4000.
https://www.notebookcheck.net/Rumored-clockspeeds-leak-for-4-8-GHz-AMD-Ryzen-9-3900XT-4-7-GHz-Ryzen-7-3700XT-and-Ryzen-5-3600XT-Upclocked-Matisse-refresh-takes-on-Comet-Lake-S-i7-10700K-and-i9-10900K.466481.0.html
When they figure out the process, they produce better cores. But instead of silicon lottery room for overclocking, AMD will select best chips and sell them as XT versions. Fine for me, since I don't overclock anyway. And it's more fair -- you get what you pay for.