Ok let get right to it.
start off with a immolate
then conflag
Then you cast a soul fire. you will now have 15% haste + 30% reduced casting time.
spam incinerate
refresh immo with fel flame when needed.
cast soul fires everytime imp soul fire is off cd and boss is above 80%.
below 80% use reg rotation with fel flame and new CD's thrown in of course.
If one were to have enough haste, would it just be worth spamming soul fires the first 80% of a boss fight?