James A. Towle, Commentary on Plato: Protagoras
James A. Towle, Ed.

εἰ βούλει λαβεῖν κτἑ.: Socrates now delivers a discourse of considerable length; but the subject excludes the brevity of question and answer, and moreover he does this with the assent of Protagoras and upon the urgent request of the others (ἐκελευέτην πάνυ).

ὃ σὺ λέγεις τοῦτο: cf. 338 e as you suggest. Similarly Gorg. 514 e τὸ λεγόμενον δὴ τοῦτο.

Prodicus and Hippias unite in strongly urging Socrates, perhaps because they hope he will humble their rival. The reflections of the seven wise men upon government and morals, and their efforts to regulate these, were expressed in sententious proverbs. This tendency to put their thoughts into pithy, striking sentences was a characteristic also of the vigorous Spartans. (Plut. Ἀποφθέγματα λακωνικά ii. 208 b ff.). Socrates makes use of this, by a keen stroke of wit, to surpass the paradoxical description of Protagoras (316 d),—to which he had already given a thrust (341 a),—by one still more paradoxical, in describing Crete and Lacedaemon, which were in fact strangers to all learning, as the most ancient seats of philosophy. This is also a hit at the imitators of the Spartans.