The blade on my Buck 119 model is 6" long which I feel is about the most useful maximum length for me.
I could go with a shorter knife blade which I did with the recent purchase of 2 Mora Clippers, however the Buck will probably continue to be my most used. Not because of the length, rather it fits my hand great and after 12 years of ownership, I am very comfortable using it.
What you're comfortable and experienced with is an extremely important factor.
For me, a blade around 4" is an extension of the hand. I work around the limitations of that blade (obviously no chopping!) by selecting the jobs that I need to do. The flip side of
"the right tool for the job" is choosing
"the right job for the tool". Around here, there's plenty of small diameter stuff to work with, both green wood and dead wood. In a survival scenario, I see no need to attack bigger diameter stuff - a 1" or 1.5" pole is long and strong enough for most shelter building, and dead firewood is usually around. And if I foresee a bigger job for a camping trip or whatever I will bring along the right tools for those jobs.
I learned the 4" lesson by making the wrong selection of a very appreciated gift from my beloved wife. She knows how picky I am. I was in doubt, but selected a 5" knife from Helle (Jegermester from
this catalog, scroll down). The handle fits my hand like a glove, the blade is razor sharp (and I can keep it that way, easily!) ... but just an inch too long. I have used it for a couple of years, but it will never be the extension of my hand a 4" blade is (such as the mora 511). So why did I pick the 5" blade? Apart from not knowing better... a 5" blade works much better than a 4" for slicing bread! Probably the silliest reason EVER for selecting an outdoors knife. Sometimes it takes a misplaced buy to learn your lesson. If there is an easy way of shortening it without ruining the temper I would do it.
The big Leuku's have long traditions for the Sami people of this area. Traditionally, they would carry three knives: The big ones (7-10") for general purpose camp chopping, a smaller knife (3-4") for slaughter, skinning and delicate woodwork and a special tiny knife for marking the ears of their rain deer and other special detailed work. I have an 8" Stromeng (
Ragnars Ragweed catalogue).
Frankly, I am still struggling to see the utility of this 8" leuku. It is somewhere between a light and short machete and a stout chopper, but too little of either to find much love in my book. And I have carried and used and abused it quite a bit, more out of stubbornness than anything else. I like the handle, I like the balance but the cutting and chopping performance just isn't that great - and clearly doesn't justify the bulk and the weight for me. There is probably some ancient secret that I am missing (lots of people LOVE this kind of knives,
example), but it just doesn't cut it for me.