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Hyperthreading is an Intel Processor method where a single core CPU is seen as two CPU by the operating system.

Now I thought my Dual CPU Xeon 3.6GHz computer would have been loads faster crunching the Science work but with HT enabled the Milkyway work takes twice as long per virtual CPU as by Dual-Core 3.0GHz computer per core.
Also the SETI working units take 2 hours longer that my computer with dual 3.2GHz Xeon. The 3.2GHz Xeons use older slower technology that the 3.6GHz later Xeons.

I've just turned off Hyperthreading and can see the times for the work units dropping rapidly so I need to see what the times are now before deciding which gets the most work done.

I did read about power levels being higher using HT and I know that it does use alot more power that the Dual-core PC. Both are set to run 100% on the science work but the Dual-core uses about half the electrical power of the Dual 3.6GHz PC.

I'm even considering selling the 3.6GHz Xeon PC and getting another Dual-Core.

Anybody have any experience with HT enabled PCs ?
Worth noting that Intel did drop HT on all CPU but have reintroduced it with the new i7 series.

Well the results are interesting.
The Milkyway work units are completing in 56 minutes now compared to 1 Hour 54 Minutes with HT.
SETI work units are over an hour faster without HT.

So from what I can see for doing the Milkyway work there's no advantage to using HT.
But as the times haven't halfed on SETI being able to run more tasks at a slower rate might be better. EG 4 units completing each completing in say 5h 52m compare to 2 unit each completing in 4h 10m.

Further -
Now things have settled down with the new settings SETI completes in around 3h48m while milkyway completes in around 52m.

The benchmarks though have dropped a lot they now report 1836 (Floating Point) and 2812 (Integer).
Now compared 1706 / 3126 for the older 3.2GHz Xeon.
And 3185 / 6465 for the E5200 (2.5GHz) overclocked at 3GHz.

With HT each CPU returns 2000+/3100+

Note all are quoted as per CPU regardless of whether they are logical or physical.

Dual core = 2 CPU .HT CPU (HT enabled) single core = 2 CPU. Quad core = 4 CPU.