Naturally by typing this next sentence I'm damning myself to a life ofpain. Mail::Thread appears to be fixed. It was creating little parent loops, in which messages became their own ancestors. By employing a quick look through the family photo album we can prevent such calamities. Doc Brown would be proud.
Did a full mariachi run on 2001-london.pm, it took ~1000 seconds. Fiddled with the templates so they show less thread context with each message, reran, it took 272.718 seconds (we so love those over-precise timings).
Took the time to breathe out.