Fionwe raised a nice point in another post, a point that I've thought about before and agree with. It's also a nice introduction of skill into a strength debate.

challenging Lews Therin's power

LOC (The Taking) - That shield made his eyes bulge, it was impossible. No three women could block him from the Source once he had taken hold of saidin, not unless they were as strong as Semirhage or Mesanna … Rand felt the blood drain from his face. Four sets of eyes in four ageless faces examined him.

Rand didn't know what was happening until he was shielded. At that stage he couldn't believe that three women had shielded him - from Lews Therin's memories he knows this to be impossible. We know that Lanfear can shield him if he merely sits there (TFOH - Choice), and this confirms his statement that Semirhage or Mesaana would have to be present to cut him off from saidin if he just sat there. We also know that Verin and Alanna linked cannot shield him.Alternatively, it would take at least 4 women linked to slice his connection, and likely more. Four strong women most likely, especially because his statement implies that three women of any strength lower than Semirhage's i.e. Egwene, would not be able to slice his connection. This would translate into a circle of a considerably larger size if those women were of average strength.

If he fights back

LOC (The Mirror of Mists) - Not strong enough. Even with the angreal, maybe not strong enough, not to hold seven. You fool! You waited too long! Too dangerous! … Shielding anyone did take a fair amount of strength. With the angreal, Rand was sure he could make seven shields, even with them embracing saidar already.

Lews Therin is quite sure that he's not strong enough unaided to shield six women at once. However, to shield six he'd need to exceed each of their strengths considerably to cut them off from saidar - that's basic shielding 101. Most likely, if he's not talking about shields he can handle more than six women strength for strength, and with his skill. The Aes Sedai are sure that six cannot take Rand, or challenge him...

ACoS (The Sending) - What I do not understand is how they captured him … Perrin, both Elora and Ledar say that when Aes Sedai find a man of great power, they always gather thirteen to take him… they wrote of Yurian Stoneboww and Guaire Amalasan. Of Raolin Darksbane and Davian, as well, but the others are who worry me… Those were four of the most powerful among the men who had called themselves the Dragon Reborn … Six Aes Sedai tried to capture Stonebow, and he killed three and captured the others himself. Six tried to take Amalasan; he killed one and stilled two more. Surely Rand is as strong as Stonebow or Amalasan. Are there really only six ahead of us? It would explain much.

.. and..

ACoS (the Sending) - “He’s being held prisoner. An Aes Sedai named Coiren and at least five others are taking him to Tar Valon…” “Six? … Six could not take him. I am sure of it.”

It seems that False Dragons and men of great power rarely fall to six women under any circumstances. Verin and Alanna think about what's necessary to take Rand...

LOC (Lessons and Teachers) - … it had been a series of extremely bad moments, from discovering that they could not cut him off from the True Source to the contemptuous ease with which he had shielded them, snapping their connections to saidar like thread. Both of them at once. Remarkable. How many would it take to shield and hold him? The full thirteen? That was only tradition, but it might be necessary with him.

We know he can't resist thirteen...

TFoH (Pale Shadows) - “And when they take the circle to thirteen, then you must be wary. Thirteen women who can barely channel could overpower most men, linked. The thirteen weakest women in the Tower could overpower you or any man, and barely breathe hard.”

TFoH (News comes to Cairhien) - Thirteen of the weakest Aes Sedai could overwhelm him linked, and he did not think that Elaida would send her weakest.

In TGS he draws lightly on the Choedan Kal and states in TGS (A Halo of Blackness) - "I'm only holding a little extra, as a precaution"... The more of the One Power a person held, the more difficult it was to shield them. If the damane tried to capture him, they would be shocked by his resilience. He might be able to resist a full circle.

This sort of hints that his unaided ability falls only a little short of thirteen women linked. I'm not saying that's his strength - merely that Lews Therin can probably fight up to 12 women without being squashed using a combination of high strength and skill. His idea that merely holding a small amount extra makes him able to resist a whole circle is rather informative.

Summary

I think the following possibly true regarding Lews Therin, to some vague degree...

1. To shield him once he'd holding saidin...
- At least 4 women but probably far more
- One of the Forsaken

2. To overwhelm him in a duel
- More than 6 women and probably closer to thirteen
- One of the Forsaken with fewer women (Lanfear wanted Graendal and Rahvin with her, which is a telling sign)

I'm hoping this will be more of a skill debate than a strength one, but my personal translation to his statements are as follows... To defeat Lews Therin convincingly you'd need the following circles...

- Lanfear and three Aes Sedai
- Semirhage/Graendal/Nynaeve and four Aes Sedai
- Egwene + Aviendha + Elayne + Metarra together
- Egwene and six Aes Sedai
- at least eight women

I think it would take the strength of at least eight women to defeat Rand, depending on their skill. If someone very skilled was in charge you could get away with eight, but someone inexperienced would need up to thirteen I'd estimate.

The point is that to defeat a man like Lews Therin you need a much higher strength than his - not an equal strength. This is very similar to Cyndane, who could fight a much stronger opponent using her skill and strength. Of course, Demandred was forced off by a circle of three, but I think mixed links give enormous power to the circle, so he basically fought much more than that.

Short summary...

1<--safe-->6<--challenge-->8<--danger-->12<--overwhelmed-->13