I got my 4 piece today. (http://us.battle.net/wow/en/characte...ouken/advanced)
Since I couldn't find a clear answer to which to use anywhere, I decided to run simcrafts myself.
Fast explaination of results: Regular rotation is always better.
Long explaination: I used mind_spike,if=pet.shadow_fiend.active this was anywhere from 700-400 dps loss depending on reforging. Higher values of mastery lowered the dps gap, highest I went to was around 2k mastery which resulted in the lowest DPS loss.
I than tried mind_spike,if=pet.shadow_fiend.active&buff.dark_archangel.up (during shadow fiend with archangel up only), this resuled in only 500-200 DPS loss in respective refroge sets.
Later I tried 2 other ways, where I delayed either shadow fiend or archangel in the sim to line them up perfectly every time. This resulted in around 800-500 dps loss.
So basicly what I learned from this; that you need some unreasonably high mastery value (probably around 4k) for mind spike rotation to be better. We should prolly stick to mind spiking stuff that dies in less than 15 seconds only.
On an unrelated note... if you are in a raid where you do not get DI reliably, once you get 4 piece reforging to Mastery will probably increase your dps (Check with your own gear set.)
With the gear I have now I found that having all buff except DI/FM, my stat weight become Mastery > Crit > Haste (with a significant difference in values between them.) Once you gain DI however, the stat weight go back to Haste>Crit>Mastery (with all of them being worth almost the same)
Best DPS reforge I found is 1742 hit, 1601+ haste (ImpPlague break point, worth ~200dps) and than Mastery > Crit > Haste. Gained around 150 dps reforging out of haste to mastery.
PS: Variable Pulse Lightning Capacitor 384 is still >>> 391 Necromantic Focus by about 100 DPS