About DE Sidious, the reason I would say put Revan and Kreia at about the same level is... Both he and Kreia are superior to Revan in the force, but it seems that Revan is superior with a lightsaber (assuming the minimal about Revan he could be more powerful then the two but we don't know)
seeing as VS fights between those would always be some what of a coin flip I would say rate them at about the same level...
Tulak and Ajunta are indeed unknowns, but Simus isn't he should have been added, although I can understand how you forgot about him and how you refused to enter Ajunta and Tulak...
Sion, well he was impressive with the force, I mean that nice little feat of holding his body together could not have been easy, he's the only one that has ever done it. And it would have been very hard. He shows great skill because of that. And because of the fact that he can't really die I would put him above both Vader and Dooku, perhaps he's better with a lightsaber we don't know, but we do know that those guys would never take him out. While he could take them out.