I like "Go Big" best of all in concept, except I wonder if you could ever go big enough. With a fairly unified country and resistance, go big could work. But there are too many factions with to much internal drive and too much outside support to be comfortable with final success. Of course, that also porks the whole "Go Long" thing.
IMO, the only way to keep the unnatural and artificial creation that is Iraq together involves: "Back to the Future." We install a cruel dictator with perhaps a Baathist flavor and turn a blind eye while he cleans house.
Making more sense, is the old but often ignored concept of "Divide and Conquer," where we slice up Iraq into three common sense parts and try to work out some resource sharing scheme. For a downside, the Turks would hate it and the Iranians would influence most of the wealth and stability could not be assured.
Cut and run may make the most sense, unfortunately, especially if we focus those resources on Afghanistan, which has fewer divisions and may still be winnable.
Charon