I would put Vestara on the same level of Mara and a little bit of Tahiri. She uses the dark side, but not fully corrupted. She was never taught the "rule of two" principle. I'm not sure she would sacrifice her friend or kill her Master [Lady Rhea] to achieve Sith Lord status. And the whole concept of Sith Saber just disgusts me.
Is it just me, if one of these new Sith faced someone of Revan, Bane, Sidious, hell even Caedus's power, they wouldn't stand a chance. It is because they don't know the "rule of two." In order for the Sith to remain strong, there must be two at any given time. Otherwise, they turn on each other like a pack of rabid dogs.