I would make my list more like this:

1 Lanfear, possibly Sharina &/or Alivia
2 Cyndane, possibly Sharina & Alivia
3 Graendal, Nynaeve
4 Semirhage, Someryn, Talaan
5 Mesaana
6 Moghedien

Lanfear's position is given. Cyndane's second, partly because I believe she's needed for the 6 stronger than Nyn (without adding too many new names to the list), and partly because she's stronger than Graendal, and I believe that Graendal is strong.

I've noticed that many people have questioned that placement of Cyndane, because it would make no real difference and thus, plot-wise, it doesn't make any sense. I do, however, believe that having Cyndane still being one of the strongest more proves how much stronger Lanfear was - if she can be weakened, and still be extremely strong, it's quite a statement to her original strength.

Since we now know that only 6 women are stronger than Nyaneve, and that she's probably stronger than Semirhage, even if it's a close call, that means Nyn is either on level 4 or 3. It might be that she's at the bottom of the 3rd, and Semirhage is at the top of the 4th. Or that they are both 3's, but with a slight difference in strength. I've decided to place Nynaeve on 3 and Semi on 4, but I'm definitely open to alternate solutions.

I do not believe that Graendal's thoughts about Cyndane were exagerration. I cannot quantify it, since it's more a feeling than anything else, though. I've chosen to put her at level 3, since my interpretation of her encounter with Someryn is that Someryin is not stronger than her. "Not negligible" doesn't sound like a "OMG she's stronger than me!" but more like a "She's strong enough that she might be a threat, but isn't one right now". If the were of equal strength, or if Someryn were stronger, Graendal should have felt more alarmed by the encounter, especially considering her reaction to Cyndane being stronger - almost as if she had been slapped in the face, with all the "very few were ever stronger than me"-attitude. Since there was no such attitude towards Someryn, my guess is that she's weaker, but not by much.

Concerning Talaan, I agree with those who claim that she's closer to her potential than Nynaeve, since she's been actively channelling a lot for several years more, and it's possible that the Windfinders push their students harder than Nynaeve has been pushed, since she hasn't been pushed at all until late in the series. So I've placed her one level below Nyaneve, but I would not argue against the two of them having the same potential.

Since we haven't seen any comparison between Sharina and Alivia, I've chosen to put them either at level 1 or 2. I don't think they're both on level 1 - either both are on 2, or there's one on each. I definitely don't see anything unreasonable with placing another channeller at the female maximum - Lanfear can't be the ONLY one ever to have been that strong. But I doubt we'll see many more there. Either way, we just don't know anything else than the fact that they're both stronger than Nynaeve. That Alivia was referred to as "significantly stronger" doesn't feel quite relevant - what's significant or not is an opinion, not pure fact.

On level 5 we have Mesaana, since BS mentioned that she's weak by Forsaken standards, but she's still stronger than Moghedien, who's at 6.