There has been a relatively longstanding debate between various gamers and overclockers about the performance of modern intel HyperThreading (HT). One group has suggested that turning off hyperthreading improves performance in gaming and results in lower temperatures and voltage thus allowing higher overclocks. The pro HT group points out the modest improvement in highly threaded workloads.
However, in light of Spectre its time to shut down HyperThreading from your bios.
Spectre attacks HT branch prediction, so you can either use Spectre fixes which will hurt the theoretical improvements of HT, or you can shut off HT and go for slightly higher overclocks or perhaps lower your voltage a bit to improve long term reliability of your chip and get better stability.
Today after much research I pulled the plug on hyperthreading, especially with the new higher core count processors, it really does not make a performance increase in most daily situations aside from perhaps CPU video encoding which should be done on a GPU if possible anyway.
So I recommend to everyone in light of spectre shut down hyperthreading, no matter what the official "marketing speak" from Intel suggests about fixes and how hyperthreading isn't terrible. (I would still implement any spectre fixes though)