I don't know the exact terrain but even on flat ground that sounds like a quite a distance to me, hats of to the both of you. I carried 22kg on my last trip, which was way to much for me (I'm only 5'7" @65kg!). So I came back with calcaneal spur and couldn't hike much for the next 16 months, lol. I think 3,5" is the perfect size for a small do-everything-knife personally, but it depends on what other gear you take with you I guess. I only carried a wood stove to cook on so I needed to be able to do some wood-processing at least. One tip though, as soon as you get there buy some of this stuff: The mosquito there are relentless and this stuff keeps them away much longer than any Deet product I've tried. It's about 5 bucks for a tiny bottle and it lasts a long time, I still didn't manage to empty mine after 2 years of mosquito summers.