A theological critique of the "Quest for the historical Jesus"?

John Webster writes:

'Knowledge of Jesus Christ is possible and legitimate because of his antecedent, gratuitous and utterly real self-presence. Setting himself forth, expounding himself as the present one who encloses and orders all things, Jesus Christ makes himself known, and thereby excludes the possibility of legitimate, well-founded ignorance of himself. He is, and therefore he is present, and therefore he is known. There is a negative inference to be drawn here, namely that this given presence of Christ excludes ways of approaching the task of Christology in which there lurks the assumption that Jesus Christ is not, or may not, or cannot be present to us. Jesus Christ's givenness sits I'll well with, for example, those Christologies which make historical scepticism or probabilistic reasoning into the first principle of the knowledge of Christ ... Because he is who he is, and because he acts as he acts in his majestic self-presentation, he cannot be "sought". That is, he cannot be approached as if he were an elusive figure, absent from us, locked in transcendence or buried in the past, and only to be discovered through the exercise of human ingenuity ... All such strategies, whether in biblical scholarship or philosophical and dogmatic theology, are in the end methodologically sophisticated forms of infidelity. Their assumption is that he is not present unless demonstrably present - present, that is, to undisturbed and unconverted reason' (John Webster, "Prolegomena to Christology: Four Theses", in the utterly brilliant Confessing God. Essays in Christian Dogmatics II (T & T Clark, London, 2005, pp. 136-38)

If Webster is right, then what is the place for certain issues raised by NT study, such that it can be reasonably doubted that Jesus did or said 'such and such' in John or the Synoptics. How would such historical findings shape the fundamentally given nature of the knowledge of Christ? Could it? Does Webster's position ultimately make study of the NT, in so far as it raises christologically-relevant questions of historicity, redundant?

His own understanding about the role of Jesus in revelation sounds remarkably Johaninne, yet apart from the growing number of scholars such as Paul Anderson, most would still prefer the synoptic presentation of Jesus. As E.P. Sanders writes, for example, in The Historical Figure of Jesus:

'[F]or the last 150 or so years scholars have had to choose [between the Synoptics on the one hand, and John on the other]. They have almost unanimously, and I think entirely correctly, concluded that the teaching of the historical Jesus is to be sought in the synoptic gospels and that John represents an advanced theological development, in which meditations on the person and work of Christ are presented in the first person, as if Jesus said them’.

If historicity is vital (and the Word, as John puts it, did become Flesh - not a text), then is there not a problem for Christology, even one that simply sits humbly before the canonical texts, because of the sometimes either-or nature of Christology in terms of the John vs. Synoptic differences?

Surely somebody out there can cleverly illuminate my thinking!