He's definitely Above DoE Bane, who's already pretty impressive. I can't see him losing to Vader, but I can't see him beating Kun or Krayt. There just aren't enough feats or accolades as previous members have said. He can block flames, and hold up rocks that are big enough to crush a ship, and is a known lightsaber enthusiast. We also know he and Plaguies replicated the Kursid Warrior feat beforehand.
I still subscribe to the theory that he let Plaguies kill him for his maxichlorian plan. substantiated by The Tenebrous Way and this odd line here in which Plaguies thinks to himself that Tenebrous not sensing his killing intent was a sign of sluggishness,
His success in bringing the ceiling down on Tenebrous was proof enough that the Bith had grown sluggish and expendable. Otherwise, he would have divined the true source of the danger he had sensed, and Plagueis would be the one pressed to the floor of the grotto, head cracked open like an egg and chest cavity pierced by the pointed end of a fallen stalactite.[/B]
Overall, I rank him pretty high, but my analysis won't be complete until I finish rereading the Darth Bane Trilogy.