Darth Bane and powerscaling
For a millennium, the Sith maintained the order in secrecy, passing down their evil heritage. As they gained knowledge of the dark side of the Force, their powers increased with each generation.
Source: Epsidode 1: The Phantom Menace Scrapbook
This is one of the sources for the idea that Bane is the weakest of the Banite line, which sort of makes sense given the point of the Rule of Two. I agree with Tempest that sort of thematic hierarchies are more consistent than feats or even accolades, and so I base my assessment of Bane mainly on this.
As I've guesstimated before, there are a lot of apprentice-master RoT transitions where the apprentice faces the master in single combat and wins. Ergo, the apprentice must surpass the master by substantial enough margin for this transition to consistently happen, and then probably continues to grow in power. We can imagine, then, that a 5% gap growth per generation would actually be fairly conservative, and given Plagueis's estimate (IIRC) of 30 sith between Bane and Sidious, Palpatine should have quadrupled Bane's power. Of course, we don't really gain much from these numbers since we don't know how significant of a disparity a % difference actually is; the more general idea is that if a one generation gap is enough for the apprentice to have a noticeably greater chance of victory (enough that the apprentice's triumph is a consistent outcome), and we compound this thirty times, by the time we reach Sidious, we've come so far from Darth Bane that Palpatine could probably one-shot him.
That's why I put Bane waaaaaay below Sidious, and probably incredibly below Dooku and Vader. I think that if you put him at Qui-Gon's level, you might get enough of a gap between Jinn and Sidious for thirty generations of power creeping.
There are a few other methods, but they're a lot fuzzier. Bane's performance against dozens of tukata is much more impressive than AotC Anakin and Obi Wan's, and he was near death and far from his prime. However, he was also on a dark side nexus, and frankly we can throw so many other things back at him, like how he struggles against X or Y fodder opponents (mercenaries, shadow guards who were stated to be "no match" for Jedi, etc.) that Anakin/Obi Wan trash with ease, that I don't take this to be a very reliable measure. His near-death and desperate state might have actually helped him draw on the dark side for a powerful wave or something.
He also mind-f*cks Andeddu's holocron which in other sources is revealed to actually contain his spirit (Drew probably didn't know this lol), but spirits tend to be weaker than their living incarnations, and we don't know much about Andeddu beyond his getting easily beaten by Wyrlock or whatever and apparently being adulated by Dooku, probably more for his esoteric knowledge than raw power.
So I currently have Bane around Qui Gon level, but I could see arguments for anywhere to RotS Obi Wan. If we used tukata scaling we could put him beyond RotS Anakin, but frankly that isn't the most reliable way of doing things.