OpenBSD was also one of the first operating systems to disable hyper-threading by default due to all the related security issues with this technology. Yet another case of security over speed.
Hyper-threading, at least in the beginning, had limited if any performance improvement when enabled. Windows (XP, 7), at least, was faster at work with hyper-threading disabled.
I'm still waiting for benchmarks which show more than a 5% increase in performance with hyper-threading enabled.
If you haven't seen a >5% performance improvement for any workload with HT/SMT enabled, you're just willfully blinding yourself to benchmark data. It can be closer to 80% than 5%, at least for some reasonable workloads.
I'm still waiting for benchmarks which show more than a 5% increase in performance with hyper-threading enabled.