XSUPREMEXSKILLZ
The Immortal Emperor
Anyways, I'm assuming the matchups are something like:
Thanaton vs. Ventress: Thanaton should win. While Ventress is certainly the more accomplished duelist of the two, Thanaton's force powers are too overwhelming, evidenced by his telepathic slaughtering of Act 1 Nox, (who at the time was being amped by two ancient sith spirits,) along with his lightning feats.
Marr vs. Maul: Marr is implied to be an extremely powerful sith lord, but Maul's concrete feats give him the edge here. Realistically not a stomp, though.
Scourge vs. Dooku: Dooku. While Scourge has a wide breadth of combat experience, amps, and implied ability, he's never come across an opponent that's concretely as powerful or skilled as Dooku, and won, nor has he defeated opponents on the level of those Dooku has defeated. Again, it probably isn't a stomp.
Vader vs. Malgus: Vader's sheer strength in TK is superior to Malgus's, though not by as much as most think. Vader has rarely, if ever, telekinetically manipulated or ragdolled a notably powerful force user. On the other hand, Malgus has thrown around the likes of Aryn Leneer, who ragdolled a six car tram, and survived a fall from coruscant's atmosphere via the force, (something even Orbalisk Bane struggled to do.) And then of course there's his infamous feat in which he annihilated a jedi master capable of collapsing large buildings via TK. Furthermore, all of this occurred far before Malgus peaked in power. That said, Vader's TK feats such as destroying an AT-AT, crushing TIE Fighters into balls, ragdolling enormous trees, collapsing a cathedral etc. are more impressive than Malgus's feats in the same regard. While Vader's raw TK feats are more impressive, I doubt he'll be ragdolling FE Malgus. In sabers, Vader's got the better accolades, but I may argue Malgus has the better feats. Defeating the battlemaster of the jedi order as a sith apprentice, (also being considered one of the top warriors in the empire during this time,) utterly outdueling Satele Shan, defeating Ven Zallow, (who was blitzing the most elite sith warriors in the empire,) etc. is better than defeating above average jedi, stalemating Galen Marek, stalemating Old Ben, being solidly outdueled by Maul's clone, stalemating ROTJ Luke, etc. Furthermore, Malgus's huge increase in power would point to improvements as a duelist as well due to sheer strength/speed boost. Add all this to the fact that Malgus has extremely powerful force lightning/force maelstrom, and I may very well side with Malgus, albeit in an extremely close fight.
Overall: Eh.