Very difficult to say. I think most women in the hugest sizes are just guessing or something. I have met women who I thought were gigantic, but not as big as someone else I had known, but they used a larger bra size that I just know they didn't buy off the rack. The largest I have been told by a woman was a lady with implants who said she was a 38T, but she also told me once she was a 38P, so maybe I did not hear her right once. Either way no doubt she was beyond huge.
Largest natural lady was guessing. She said she had been told she was a 34NN but who knows. Both women had bras that were made by hand.
Not all women with huge breasts are great lovers. Some had small pussies and that never works.
But all the women with really huge breasts really enjoyed the visual and physical, as did I, of my erection between their cleavage.