I'm probably missing something, or maybe doing something wrong, however I've noted that when compared to a non botting similarly geared shadow priest, specced for insanity, I normally am mind bender with 4/4 t18, that I will meet or exceed their dps, however when I spec insanity they end up doing more dps / dmg overall. I've gone so far as to stand near them and take note to how often we move to be as close as possible to straight up rotation. Only thing I have been able to tell with similar number of casts, 30 vs 31 in one encounter, that my insanity ended up having an uptime of something like 25-34% where theirs was more around 92%, which then showed on the meters. It was the kormrok fight I was using CoP with CoP standard.
Hoping to get some more understanding on if Insanity is the way to go or if I should ignore for mind bender, as it's a set it and forget it dot basically every 20 seconds, however it seems like a lot of the higher tiered SP's are running insanity, so I'm torn and conflicted.