You can strip down to 30lb of clothes, food and cooking utensils for a 4 day hike and keep it going at a steady 6k/h clip on roads and 4k/h on offroad.

At least that was what i used to do for DoE expeditions. I would say that is a fair estimation of an averagely fit person's carrying capacity, though I did have a tendancy to strip out any extras or luxuries (spare clothes, bah, I'll just dry em overnight!)