>  From my personal bench with povray, a HT-core is worth between 20 to
> 25% of a real core. (tests done on i7 980X, at nominal speed, with
> benchmark scene)

This is on Win 7 with the standard POV binary, the benchmark scene and a 
Xeon E5-1650 @ nominal speed.

> beware, when comparing with time, the performance is 1/time.
>
> your 6 threads has a performance index of 5.20833, about 0.868 per thread
> your 12 threads has one of 7.35, about .613 per threads.
> (and if you remove the 5.208 from the 7.35, the additional HT-core only
> provides 2.142, that's 0.357 per HT-core, so a HT-core thread is in your
> system about 41% of a real core thread, for povray-binary and your scene).

Yes, I think the additional HT'd threads being worth 41% of a real core 
thread, is the same thing as saying that if you only use the real cores 
you're utilising about 70% of the total CPU performance available. I 
assume that modern compilers optimise code to be hyperthread nicely?

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