I recall James McGrath asking how to gauge scholarly opinion on the pseudonymity of the Pastorals (1 Timothy, 2 Timothy, Titus). On the one hand, the commentary tradition is pretty evenly divided and you have a number of major commentaries defending authenticity (Gordon Fee ; Donald Guthrie ; J.N.D. Kelly ; George W. Knight III ; William D. Mounce ; Luke Timothy Johnson ; Ben Witherington ; Philip H. Towner  etc); on the other hand, commentaries are often geared towards a conservative market and I think James is right that one of the signs of scholarly consensus is that pseudonymity is mostly taken for granted while any monograph, SBL presentation, etc would not be able to just proceed on the basis that Paul wrote these letters without first defending their authenticity. I suspect a similar thing is at work with the nearly unanimous support for Markan priority (whether scholars accept the Two Documentary Hypothesis, the Farrer theory or more chaotic approaches). It is not that there are not able scholars who have challenged Markan priority (e.g. William Farmer), but anyone who makes an argument about the gospels or the historical Jesus that rests on a different solution to the Synoptic Problem is going to have to make a strong case for an alternative. One sign of this consensus is that, of all the commentaries I listed here, the vast majority start from the premise of Markan priority. The one significant exception I can think of is C.S. Mann’s commentary on Mark for the Anchor Bible series that worked on the basis of the Griesbach hypothesis, but it has since been replaced by Joel Marcus’s two-volume commentaries that support Markan priority (Mark 1-8, pp. 40-47). A “consensus” can always be overturned, but to defeat a reigning paradigm one must (1) poke enough holes into its main arguments and (2) present enough counter-arguments to suggest another solution is more probable.