Nigel:
It's a fair question. I don't know the answer yet, because my research for Volume 2 will come over the next two winters -- I still haven't seen any of the courses mentioned in Mississippi, Louisiana, Arkansas, or for that matter Wyoming. Scouting reports indicate that most of these states have a course or two that is a contender for a 6.
There are three states where I have played some of the contenders and have yet to award a 6: New Hampshire, Kentucky, and Iowa. Wakonda would be a 6 if they fixed it up, but they haven't. Valhalla would be a 6 for most people, just not me. I've also yet to decide whether any of the courses I played on the North Dakota Golf Trail really deserve a 6 ... they will need to catch me in a generous mood.
P.S. I don't intend to go to Alaska at all, unless my wife wants to.