In contrast to the last quote (and my own view falls somewhere between these two extremes), here's Frans Neirynck, "Paul and the Sayings of Jesus":
In the Pauline epistles there are two instances of an explicit reference to a command of the Lord, in 1 Cor 7,10-11 and 9,14, but there is not "quotation" of the saying... and [these] can scarcely allow for any general conclusion about Paul's acquaintance with the sayings of Jesus.
Elsewhere in the Pauline letters there is no certain trace of a conscious use of sayings of Jesus. Possible allusions to gospel sayings can be noted on the basis of form and context but a direct use of a gospel saying in the form it has been preserved in the synoptic gospels is hardly provable. Paul's knowledge of a pre-synoptic gospel, of the Q-source or pre-Q collections has not yet been demonstrated. Because of the paucity and the anonymity of the possible allusions and reminiscences, and because of their appearance together with other ethical teaching in the paraenetic sections, it remains doubtful whether Paul was using them as sayings of Jesus. (in L'Apôtre Paul: Personalité, Style, et Conception du Ministère, edited by A. Vanhoye, pg. 320)