Telling Characters Apart

Day three of revision work on City of the Saints, and I think it's going well.

City has six POV characters, and I want each of them to sound distinctive in his speech and feel distinctive in his POV.  What are some of my tools?

• Vocabulary (some think; others reckon).
• Elision and contractions (for some it's not; for others it ain't).
• Oaths (Jumpin' Jehoshaphat! Rostam's mace!  Jebus!  Egad!).
• Wordiness.  Correctness and precision of grammar.
• Slang (one character is a carny).
• Use of foreign words or phrases.
• Long versus short words.
• Subject matter obsession.
• Lyricism vs. prosaicness.
• Gnomic speech, folk wisdom.
• Interjections and contentless words, er, that is to say, et cetera.
• Speech impediments (at one point, one of my characters gets his dose broked).
• Specific memories / references unique to the character.