Can you share what the theorycrafting came up with? I would go with more mages than shadow priests. I am not sure what benefit multiple shadow priests have. Desecration should keep Torment the Weak constant which is a good thing synergy wise (on stuff that is actually impacted by torment, though if your slinging frost then that's mute) The ezmode replenishment of frost is quite insane, compared to the shadow priest.