In practice on Zen1 and Zen3 I found HT to provide 20% to 25%. It seems some benchmarks are as high as 50% with zen5. AMD really improved HT with Zen 5 by add

In practice on Zen1 and Zen3 I found HT to provide 20% to 25%. It seems some benchmarks are as high as 50% with zen5. AMD really improved HT with Zen 5 by adding a second instruction decoder per core. I expect even better per-thread performance from Zen 6.