The AMD Ryzen 7 3800XT and Ryzen 9 3900XT have hit 3DMark Fire Strike. Offering incremental improvements over their predecessors, it would appear that they are just better-binned versions of the Ryzen 7 3800X and Ryzen 9 3900X. Talk of 300 MHz higher base clocks and 200 MHz higher boost clocks seems unfounded, too.
https://www.notebookcheck.net/AMD-Ryzen-9-3900XT-and-Ryzen-7-3800XT-hit-3DMark-Fire-Strike-talk-of-higher-base-and-boost-clock-speeds-appears-unfounded.466902.0.html
I think the XT versions are lower binned 3900Xs with 2 active CCDs eg.
3600XT = 2 chiplets with only 3 active cores per CCD and double the cache of the 3600X.
3800XT = 2 chiplets with only 4 active cores per CCD and double the cache of the 3800X.
3900XT = 3900X with higher clocks (doubt this actually exists).
I think you are wrong. They don't have doubled cache.