the 4 holding Rand clearly must have been stronger than the 5 who could not hold Logain.

We know at least Sashalle is reasonably strong for an AS since she's taken charge in Cairhien ...

The evidence is that 5 very weak women could not contain Logain, while 4 reasonably strong women (certainly well above Siuan) held Rand. We also know that none of these women were exceptionally strong since Sahsalle is clearly the strongest of them and she is only slightly above Samitsu, who's behavior points to her being weaker than Verin ... This probably means Sashalle is similar to Verin, combined with similar strength women 4 could hold Rand. Which equates to approximately 8x Daigian holding that shield ... and as soon as it dropped to 6x Daigian he shattered it.

Then we have similar situation with Semirhage. 3 women held her shield and it was considered "taking precautions" ... at one point one of the women was Daigian! Corele and Nesune are reasonably strong, but not at the top AS levels, ... but above average so maybe 2x Daigian ... if Semirhage, who is very close to Nynaeve, could be held, easily, by these 3 that would be approximately 6x Daigian strength and it was deemed as taking extra precaution. Meaning 4x Daigian would have been sufficient to hold her, and possibly 3x since there are other combinations of women who hold the shield and same sex shielding is supposedly easier.

Point here is that Nynaeve cannot be 10x Daigian, or even 8x Daigain or she would have been able to hold the shield on Logain. Nynaeve had not reached full potential by this point, but she was pretty darn close since she was already stronger than Moghedien.