Gnomeover

Hello, first time poster here! I've been doing alot of reading and searching and had a question that I could not find the answer to. I know that as an affliction warlock about 35-36% of my dps comes from shadow bolts after all dots have been applied. I am wondering which meta gem would be more beneficial to me. Swift Starfire Diamond adds +12 damage while Mystical Skyfire Diamond reduces the cast time of my shadowbolt, immolate, and unstable affliction.

Looking at the numbers it appears that they drop below the global cooldown. So for immolate and ua (in theory) it would appear that there is zero increase in dps if I used the charge on those. However it would increase the dps of shadow bolt slightly. I am just wondering if that increase in shadow bolt dps is worth more than the 12 damage from the other meta gem. I am under the impression that sustained +12 damage over dots + shadowbolt would be much better than a few Mystical Skyfire Diamond procs. However, I would love your opinons because I am not really sure how to proove this!