Quote - ...Hyperthreading will get you a 10%-20% performance increase over a non-hyperthreaded ...

Yeh. That's one of the results I too got from my simple test above. Overall CPU utilisation (work done by all threads combined) was about 10-20% more using hyperthreading than without it (ie. when ticking the box "separate process", it basically apparently denies use of hyperthreading from the processor). Single threads operated at much lower efficiency, but the total work done exceeded that of using the cores without hyperthreading.