That it's IMO most unlikely that the DO or the Eelfinn can grant a higher OP strength. Otherwise there should have been many more super strong channelers. The Eelfinn would probably simply give you a sa'angreal, if you wished for more strength.

Lanfear just never encountered a woman stronger than her, even in the AoL. Like Rand or Ishy, I think she simply had the "luck" to be one of the strongest possible among her gender. That changed, though, when she died & got a body, which couldn't handle all her theoretical OP potential.