Should've waited to post this with either A) Sims that match the encounters you list, or B) Logs
I've been doing some in-raid testing (and I'll be doing a lot more next week). Basically it seems that in an encounter where there is little movement, like Chimeron, AND we can stand close enough for Immo aura and Shadowflame, going straight Mastery is definitely the way as far as reforging. When there is a lot of movement, e.g. P3 Al'Akir, haste seems to be a much better choice. Again, I've only tested a little (I should have a lot more info next Wednesday), but like a few other people have expressed; SimC has been quite a bit confusing since 4.1 hit.