An interesting set of stats pulled from: Mac Forums – Pentium M and Yonah Processors in Upcoming Macs?
With HT enabled, I can run two copies of the job, but they each take 3 CPU hours (and the two finish in 3 wall clock hours).
So, in a day, I can run 12 jobs without hyper-threading, or 16 jobs with hyper-threading. My Opterons do about 13 per day per CPU. (3.6 GHz/1MiB Xeon, 2.6GHz Opteron)
Is it slower with HT – by one measure, yes. Is it faster with HT – by a different measure, yes.