I'm here to tell you that while that may be the way it works out in simcraft, it certainly does not play out that way in Dragon Soul. My advice to all shadow priests reading this is to evaluate your own playstyle and make decisions on your stats based upon your strengths, weaknesses, and the encounter for which you are preparing.
In my case, Heroic Spine of Deathwing awaits my attention. For this particular fight I am stacking as much mastery as possible with the gear I have at my disposal. Roughly I am toying around in the area of 20-21 mastery, ~20% crit, and around 20% haste... hit capped. Let's face it, from a dps perspective this fight is entirely about controlling your aoe-hungry self and, instead of unleashing that raw mind searing potential, you prepare for a single-target, bursty rotation on that resilient burning tendon is active. You want to plan your rotation around a 23 second window (the total exposed time of the burning tendon you must vanquish.) For me, this involves pre-dotting various corrupted bloods with Shadow Word: Pain as they will proc shadow apparitions that will instantly give you 3 orbs while you are in rotation (as if the shadow fiend wasn't enough.)
Rotation (with SW:Ps ticking on bloods): Mind flay 2x, Bottled Wishes Trinket, Shadowfiend, Wings, Mind Blast, Mind Spike x3, Mind Blast, Mind Spike x4, Mind Blast (continue, making sure your mind blast is always used with 3 orbs). In 23 seconds on a training dummy without buffs this consistently landed me around 1 mill damage done. In a 25m raid setting with buffs (and di) this is anywhere from 1.2 to 1.5 million damage with my current setup.
The challenge with this lies in mind flaying enough to have your shadowfiend ready for the next tendon. Ugh. This fight is really awesome at making everyone have a lot to do, and yet not have a single shred of fun while doing it.
