I would guess that specifically the most heated Pit threads seem to be where poster A is accusing Poster B of lying about what poster A said. Usually these devolve into arguments about whether poster B’s statement was a fair paraphrase of what poster A actually said.
I think the Pit is a good solution for this; it’s very likely that one or both participants are going to lose their temper in such a discussion, which, if it has to stay in the original thread, is only going to lead to the thread getting hijacked and possibly people getting Warned.
For less emotionally charged situations, where someone is perceived to be lying about something not related to the personal integrity of another board member, I think it would be a good idea to tighten the moderation a bit. People who repeatedly post objectively false claims, and refuse to address the evidence presented that they are wrong, should IMO be moderated, at least in GD and P&E.