Perhaps if we did a bit of scientific empirical testing.  Anyone who has a HyperThreaded processor can do this.  It is absolutely irrelevant if your processor is not HyperThreaded.

Set up a scene of sufficient complexity to simulate a real project.  Use reasonably high render settings.  You must not change anything between the test renders except the one variable in question.

Render 1:  set the render threads to the number of cores your processor has.  Render using the script partners: Dimension3D : render Firefly and click the render (time) button.

Render 2:  set the render threads to twice the number of cores.  Render (time).

 

Poser 12, in feet.  

OSes:  Win7Prox64, Win7Ultx64

Silo Pro 2.5.6 64bit, Vue Infinite 2014.7, Genetica 4.0 Studio, UV Mapper Pro, UV Layout Pro, PhotoImpact X3, GIF Animator 5