Sarasu's also an interesting case. He's basically the result of giving a Marr-level Sith Lord power that surpasses Luke's by far... You end up with a difficult result. A Sith Lord who is relatively unskilled, unknowledgeable, and unable to otherwise put his power to use as dangerously as someone like Palpatine could, but may well be the strongest regardless...
Then again, by the time he was that powerful, he seemed barely able to move too. And if he's not the #1, well, where does that leave him exactly?
After some increased knowledge on the sith. My new list:
1. Palpatine
2. Vitiate
3. Plagueis/Kun/Krayt
4. Plagueis/Kun/Krayt
5. Plagueis/Kun/Krayt
6. Revan
7. Caedus/Vader/Bane
8. Caedus/Vader/Bane
9. Caedus/Vader/Bane
10. Hype Lords, Ragnos, Hord, Sadow etc could go anywhere on this list tbh. I want to believe they are top 5 but little info is given so I'm putting them at 10.