Fascinating and humbling.

Torture: one of the ugliest and most perverted activities of man to take place on this globe, and made even worse for the receiver if those tasked to torture enjoy it.

I've not read the whole thing but most of it. I bet that after considerable time the human physique becomes insensitive to pain. Perhaps even mentally -- if strong enough -- the pain receiver's mindset would enable him to withstand a lot.

Key, I think, would be to be both superiorly physically and mentally fit while the two keep each other strong: if one falls the probability of the other one falling increases, and when they both fall it is over. When mentality is the first to fall it's likely that the physique will fall rapidly more so than the other way around.