I don't get it, where this stuff came from with fire being greater self dps than shadow. It's *NOT*, I repeat _no it isn't_
Do the math if you like, or wonder for a second, how the best reason people had to go fire was, that "someone from SK Gaming was fire in the Brutallus video" -yup, and notice how the others were shadow (including their WWS for Brutallus). The fire guy was probably testing something aight.
And yeah, as mentioned early, just go check Elitist Jerks or Nihilum, there are several pages about this. Shadow > Fire.
Go get the Warlock DPS spreadsheet. Fire is more personal DPS, shadow is more raid DPS. This is fairly well accepted.
I think you have it backwards... fire outdoes shadow with the proper makeup. Without that proper makeup, shadow outdoes fire. With a proper raid group, you'll have enough shadow locks to keep ISB up and any extra locks can be fire to increase DPS. If you don't have enough shadow locks or have an absurd number of shadowpriests or no fire mages, then shadow can outdo fire due to increased raid utility.
Shadow locks keep ISB up for one another, making them all DPS more...fire locks, do what for each other exactly?
An overlooked problem with Fire Destruction is poor haste scaling. After reaching the required haste for a 7-Incinerate rotation, the haste up to an 8-Incinerate is not as effective as it would be for Shadow Destruction.
Incinerate may be more mana efficient than Shadow Bolt, but using Immolate makes Fire less mana-efficient.
Shadow Destruction still has a higher coefficient and thus will scale better with raw spell damage.
Not only will higher ISB uptime increase Shadow Priest DPS, it will also increase mana return from said Shadow Priests, thus increasing the DPS for other raid members as well.