The Path of Daggers, Unweaving
Talaan, so meek in her red linen blouse, with eyes that seemed permanently downcast, came very close to Nynaeve. Very close.

Talaan is probably on the same level as Nynaeve, but is clearly not stronger.

My list is closer to Sids for many of the same reasons:

1. Lanfear and possibly Alivia or Sharina
2. Cyndane and possibly Alivia or Sharina
3. Graendal and Sharina (minimum) -- Alivia cant' be this level or she wouldn't be "considerably stronger than Nynaeve"
4. Nynaeve, Talaan, Sommeryn
5. Semirhage and Mesaana
6. Moghedien, Tamela and Viendre
7. Egwene, Elayne, Aviendha and Metarra
8. Cadsuane, Bode and Nicola
9. Meylen and Kerien
10. Elle and Jancy
11. Moiraine, Elaida, Romanda, Lelaine and old Siuan

I also look at Graendal as stronger than Semhirage/Mesaana for a couple of other reasons. She stands alone and open. We know from Aran'gar that Graendal's alliances end abruptly with her "ally" dead. She's far to ballsy to be weaker than the others, she openly mocks the likes of Demandred and mentally dismisses Mesaana as a non-entity.

My other main reason for believing she is stronger is that RJ has built up quite a mythos around her. She's been the "replacement" Lanfear for a while now, the go-to for all evil femaleness.

As for her lying to herself ... yes I'm sure she does, but IMO the FS lie about their Greatness or how much they've Acheived or their incomparable Skill ... lying about something as strength in the OP is rather trivial to them, they constantly laugh about the "half-trained" girls calling themselves AS and Graendal's comments about Sommeryn were telling as well. In her mind Sommeryn was inconsequential because she wasn't well trained.

As for your Gateway thoughts, I've been saying as much for a while, I don't believe Strength can be figured out from ability with one weave. We've already seen too many examples of things like Siuan's healing being the same despite only being 1/3 as strong as she was before... Rand's 4x4 Gateway maybe impossible for anyone else to achieve even if they were stronger than Rand, if he has particular facility with the weave he can do it better... look at Berowin and her shields!