> macOS performance: Testing conducted by Apple in May 2019 showed as much as a 40% reduction in performance with tests that include multithreaded workloads and public benchmarks. Performance tests are conducted using specific Mac computers. Actual results will vary based on model, configuration, usage, and other factors.
It really is going to depend on what test you are running. HT has the greatest effect when the running process has a lot of "downtime" for things like memory retrieval or any I/O as it allows for other processes to make use of this downtime. So if your tests are just doing calculations with very little file/network I/O it could very well be in the 9% range.
from here: https://support.apple.com/en-us/HT210107