Well, I am quite familiar with the PNW, I've spent 22 of the last 25 years here. If I thought there were a chance I would have to survive more than 1 night I would have several things with me in addition to a knife, first I'd have a 19 ~ 24" saw blade with me (size varies with which pack I'd be carrying). I'd also have a hatchet or boys axe, somewhere in the 1.5 ~ 2.5 lb range, hung with the longest handle my pack would accommodate. The honest fact is that even with a BK 9 or BK 4, in a long term survival situation in this environment, processing enough wood for shelter, and heat would take up way too much effort and time with a knife, you can do it for a day or two, but not for an extended period like a month, especially if you are on the move, and have to rebuild your shelter on a daily basis. A saw and a small axe or hatchet will save you so much time and effort over a knife, that it will greatly increase your odds of surviving long term in this environment.
I chose the BK 5 (though I'm not sure I wouldn't have chosen a Potbelly if the list were opened up to other KaBars). I'm afraid that if I found myself in a long term survival scenario, I'd want a larger knife than what I normally carry (a BK 16 or smaller). I'd want a large knife that would be adaptable to detail work, I'm sure the 9, 4, and 2 could handle the detail work, but I wouldn't be as adept with them as I would be with the 5. The first such job would be to fashion a saw frame for the saw blade.
Surviving in this environment is very much about keeping dry, and keeping your core temperature in a healthy range. Local edibles are much harder to come by in the late fall and winter seasons (this is why the bears hibernate, they can't collect enough calories to stay active), so conserving energy, would be key to making it for a month outdoors here, especially this time of year.
Erik