When Soulfire got buffed 22%, it became a higher priority with Molten Core procs and Dark Soul up. If Dark Soul isn't up, you want to save Soulfire for caster form because of the higher Demonic Fury generation. Soulfire, if done properly, should appear twice on World of Logs. One form will be the one that cost a shit ton of mana (caster form) and the other one will hit a crapton harder (Meta form). Basically in Meta, your priority is this:
1) Touch of Chaos if Corruption duration < 2 sec
2) Doom if Unerring procs, cycle targets
3) Doom if not applied
4) Soulfire if Dark Soul is up
5) Touch of Chaos
Basically if Corr is about to wear off, use ToC at least once. I usually do it twice for 12 additional seconds. After that, make sure Doom is flying on everything that it will tick on at least once, especially if Unerring procs. If Dark Soul is up, use Soulfire; otherwise, use Touch of Chaos.