Is there an "Abraham Line"?

Everyone places the 'boundary of historicity', where you decide to go with the biblical text as opposed to possible evidence to the contrary, at one of these five locations:

      1. Genesis 1
      2. Genesis 12
      3. Gradually after Genesis 12
      4. After the Exile (Ezra/Nehemiah)
      5. OT = Pure fiction

I think this is a different question as to what to then do with the text.