Mark over at Pseudo-Polymath has a question for Sola Scriptura adherents. He names a variety of doctrines and asks how does a Sola Scriptura adherent decide what is in bounds and what is out of bounds.
Generally, I expect to find that someone who trusts the New Testament accounts will believe a thing if Scripture teaches it, disbelieve it if Scripture teaches against it, and is open to discussion and even varying opinions if Scripture is silent or is not explicit. In those "gray area" cases, if an early and unanimous opinion exists among the early church fathers I would expect to give that opinion the benefit of the doubt without quite holding it with the same certainty as Scripture. That's why we (Lutherans) hold to the real presence of Christ in the Eucharist (Scripture teaches it) but not to transubstantiation, and why most of us do not hold to Mary's perpetual virginity though some do.
I don't think this next was your main question, but I think the quote from Pelikan had an interesting salvo. He implied that the usual explanation for the Scripture "The Father is greater than I" amounted to "manipulation of the Scriptures". I have to agree on this much: the usual explanation of that is disappointing at least and may even cross the line to manipulation of Scripture. That particular text is often explained away as meaning that when Christ acknowledges the Father as greater he does so "according to his human nature"; yet when else is he said to speak according to human nature alone? I have always believed this interpretation to be an unnecessary and possibly misleading move. To speak in Trinitarian language, the Father is the only member of the Trinity who has no other origin but is self-existing; the Word and the Spirit both derive from the Father. "The Father is greater than I" seems a natural thing to say even for a Trinitarian: that the Word, Christ, has his origin in the Father but the Father alone is self-existing. As the self-existing source of the Son, the Father is greater than the Son. Now I will also speak bluntly: I think that such a questionable exegetical move was mainly made to defend the Trinitarian formula. I consider some parts of the Trinitarian formula to be an intellectual syncretism between the revelation of God and Greek philosophy. I know "intellectual syncretism" may be seen by some as fighting words, so let me explain what I mean. The relationship between Father, Son, and Spirit is not cleanly understood or expressed with complete clarity in the common formulas used for the Trinity. Granted that nobody has yet done better expressing the nature of God using the categories of Greek philosophy, and the standard Trinitarian formula may well be the cleanest fit possible between the nature of God and Greek philosophy. Still, certain things we know about God seem to have been squeezed a little bit to fit into those categories, and it has created a tension in Christian theology ever since. I expect the day will come when we Christians rethink the Trinity in terms more native to Scripture and that, when complete, we will still have the Trinity but not one so determined to see things through the lenses of ancient Greek thought categories. At the time the Trinity was formulated, much of the Christian world was still deeply enamored of Greek philosophy, and may have overestimated Greek philosophy's capabilities towards expressing the realities of God. Until such a day as we retool our understanding of the Trinity to go beyond that kind of intellectual syncretism, certain passages of Scripture will show their tension with how God has been fit into those pre-existing schools of thought.