Spence,
I often wonder over the forest floor who's a faster runner : a man in mocs or a man in shoes.
I can't help but think that its the latter rather than the former.
I've seen Mark Baker's rendition of hoofing it through the woods but I see that as no different than a Hollywood display.
I like to make them, I like the look of them and their different styles but I am painfully (literally) aware of the limitations of mocs.
Nock,
I haven't used Bison or Moose or chamois but I have used deer, elk, cowhide split and garment weight cowhide.
The Elk and deer have always been chrome tanned, I won't use brain tan for mocs just because its too expensive for me until I start to tan enough of my own to make that commitment.
I generally wear one pair inside another with a wool liner inside the inner pair. Elk as the outer, then deer, then wool.
One mistake I would have you avoid should you go this route is that the will need to be slightly larger as you make them from inner to outer mocs.
I believe in sewing on an outer sole I just haven't done it yet.
I won't lie, an insole between the layers somewhere is a life saver on a rocky trail.
BTW, the leather I found the least forgiving as far as stretch was the cowhide split, FYI.