If mitigations include disabling SMT and the workload is compiling code, then the difference is easily in double digits.

What OS ships the mitigation of disabling SMT by default? Surely they just meant things like the retpoline mitigations in syscalls?

my specific use case where I see significant performance improvement is image segmentation pipelines (which involve opencv-style image processing and AI inference). YMMV depending on your CPU I suppose.

Video editing maybe? Which is not going to involve running untrusted code.

It's not going to hammer on syscalls, either, so it won't have any spectre-related regressions.