In light of this, Traya is an interesting force user to consider. She neither seems 'beserker rage' or 'focused anger' - she always seemed very calm, almost serene. And yet she was a powerful practitioner of the darkside, but then again she was never really Sith. I'd say Traya is a good example of a darksider who completely mastered and honed her emotions to the point that she no longer needed to incite fear and anger to draw on the darkside...
Well, Traya was focused on her hatred of the Force itself. Since it's not a physical thing she can lash out at, she had to be calm and cunning to put together her plan to destroy such an abstract enemy.