BRBBWadmirer:
I've seen people who were mobile at a level where they could walk consistently and without assistance in the 600-pound range (maybe low 700-pound range as well), and most were pretty much what BigFox described above. Meaning male, tall, solid build, etc.
Oh wow, I mean yeah I figured depending on the person mobility is still achievable at 600, though the thought of even lower 700 too still gives some hope