2. As Socrates and his interlocutors consider the different regimes in Books VII-IX of The Republic, what is the standard of judgment they use for all of them?

It's difficult to put one's finger on just "one" standard of judgment that Socrates uses to evaluate different regimes, but the most obvious would probably be the notion of justice--a justice, of course, that is ideal and formal--revealed only in contemplation and philosphicla dialogue.