The May 15 2000 Watchtower page 4 indicated that scholars at the Jesus Seminar had concluded that 82% of all the words attributed to Jesus in the gospels were not authentic but 'derived from later tradition'.
It is difficult to say for yourself but I do find it remarkable that Pauls letters do not contain any references to Jesus' life, history or more importantly his teachings. The sermon the mount, lords prayer or the golden rule etc. etc. do not get a mention in his words to fledgling congregations. Whether the gospels were in circulation at the time of his writing his letters is unlikely,although the WTS dates Matthews gospel at 41CE. But irrespective you would expect his words to have been talked about and recorded in some form or other. For Paul or the other writers not to mention any of Jesus' words is supportive of the contention that much now attributed to Jesus has to be unreliable.
*** Rbi8 Matthew 7:28 ***
28 Now when Jesus finished these sayings, the effect was that the crowds were astounded at his way of teaching;
(You would think those 'sayings' would be worth repeating to those far away congregations that Paul wrote to that may not have heard them.)