I voted for 4x4. I always carry a knife that size, usually in pocket or belt. If I carry a larger knife at all, it is in my pack (that would be my SR battlerat). I am much more likely to carry a small axe (Granfors Bruks wildlife hatchet) than a big knife though, cuz it is way easier/efficient to chop with a good axe than a knife.

The thing is, it has to be *convenient* to carry even if you don't expect to need it (I also carry a folder for most routine cutting chores), but big *enough* to get most survival work done and a 4" blade works great in that role. 4" handle is enough, that is why I like that handle size.