barbarian brings up a great thought.
In days of old (1700's & 1800's) I wonder what folks who traveled in the less populated areas carried with them. I suspect that they weren't typically "processing wood" with a knife, but more likely they carried a saw (how common was that???), an axe (almost certainly), and splitting wedges of some kind (maybe locally fashioned out of wood???).
Ken, in "pioneer" days, most explorers, longhunters, mountain men etc. would carry both a skinning knife, similar to the Russel Green River and also a longer knife for more general or combat usage like the Rifleman's Knife or the ever famous Bowie (once it became widespread). In addition, most also carried a hatchet or tomahawk. And a lot of them had a patch knife carried on their possibles bag or around the neck.
That's just the stuff that was carried on the person. If they had pack animals, you can bet they had a felling axe and other tools on the horse!
Jeff White makes some great blades, although I don't own one (yet). I want one of his Nessmuks!
Now, on to the main question...
My latest "outdoor knife" is the TOPS Band of Brothers Fieldcraft knife. It's about 4.5" long and I wouldn't want anything longer. It's pretty thick and solid too. So far I've been able to use it for just about anything, including making fuzz sticks and carving and some heavier work. I also have an ESEE Izula II that's great for when I don't want/need the heavier blade. I also have a couple of Moras that I love, but I think I'd want something full tang for "survival" use.
So, in my opinion, those two blades cover most of what I'd need for emergency use. If I'm going camping, my hatchet/tomahawk comes along. A larger fixed blade is just extra weight and overkill in my view.