I suppose if enhanced saidar only got you to potency X, and saidar/saidin combo got you to potency Y, where Y>X, and Nynaeve judged the fireball to be potency Y, then her comments would still allow for my idea.

However ... I don't buy it . It seems clear, from your quote, that RJ wanted the reader to understand that it takes saidar & saidin combined to create the more potent fireball. And consequently that my original suggestion is wrong

Therefore, Sidious must be right - the only additional benefit a mixed circle provides over an unmixed circle is that associated with combining saidar & saidin into one weave. So (for example), if one man links with 1+ women, and only channels saidin to create a weave, that weave will be no more potent than what he could have created unlinked. Actually, it would probably be slightly less potent, due to the small loss of strength that occurs when linking.

I say "probably" because it's not 100% clear (to me, anyway) how to allocate that "link-loss" between the circle members. For example, let's say two women of strength 10 link. And let's say that, due to link-loss, the combined strength is 18 (not 20). Is that because the two women each get reduced to strength 9, or because the leader remains at 10, but the non-leader gets reduced to 8?

In that example, the answer doesn't really matter since the net effect is the same. But consider the case of 10 women of strength 10 linking. In the former case, their combined strength would be 90 (10*9). Whereas in the latter cae, their combined strength would only be 82 (10 + 9*8 ).

I think the former case is probably the right answer, but as I said I'm not 100% sure.