Is there a received view on the relation between Thrasymachus' view and that of Callicles? Is their view fundamentally the same or in some important sense different?
Wouldn't the following passage from Republic I suggest that Plato took them to be the same? The passage occurs just before Socrates gives his final three arguments against Thrasymachus:
That's a much more awkward proposition, my friend. It makes it hard to know what to say. If you said that injustice was profitable, but nevertheless admitted, as most people say, that it was wickedness, or something to be ashamed of, we would be able to make some reply along conventional lines (ta nomizomena legontes). As it is, however, you're obviously going to say that it is good and strong, and credit it with all the qualities which we used to attribute to justice, since you didn't shrink from classifying it with goodness and wisdom. (348e-349a)(Greek available here.)The view which the passage describes is exactly what Polus in the Gorgias holds: injustice is profitable but also wicked and shameful. One may refute a position like that by beginning from injustice's being shameful, and then arguing, ad hominem, that this would imply its somehow being unprofitable as well--as Socrates does in his refutation of Polus.
But, if so, then, by extension, the more consistent and therefore more problematic view, proffered by Thrasymachus, is--from Plato's view at least--philosophically on a par with that of Callicles.