Not much to go on to be honest. Naeff all we know for certain is that he was not as strong as Nynaeve (that's stated when Nynaeve and he are cleaning up the bubble of evil in Tear just before she Heals his insanity). So I put his maximum level as a 5

Narishma's minimum level is based on Merise's comments about his growing stronger, and her worry that he would become stronger than she was (level 14), implication being that he was at least equal to her currently. I placed his maximum potential at ++5 mostly to be tongue in cheek ... Sidious made a comment in an earlier post that he'd like to see people in the ++5 and ++6 so I threw some in there (False Dragon's and Narishma).

I have been adding rational into the placements, but it's ALL thin as I haven't had time to really go hunting for specific quotes beyond what's in the Companion at this point. So mostly it's based on knowing if someone could Travel or if a woman was strong enough to attain the Shawl or if she was directly compared to another woman whose strength we know. Or has a feat of the power directly comparable to another whose strength we know.