Forget that in Legion I'll just have to relearn everything anyways, but... This is my current rotation:
--Phase One--
1) Spam Mind Spike
2) Use Mind Blast on cooldown
2) Enter Phase 2 at 5/5 Shadow Orbs
--Phase Two--
1)Apply Vampiric Touch
2)Apply SW: Pain
3)Apply Devouring Plague reducing you to 2/5 shadow orbs
4)SW: Insanity as long as you can
5) Mind Blast to bring you to 3/5 shadow orbs
6)Apply Devouring Plague, reducing you to 0/5 shadow orbs
7)SW: Insanity as long as you can
9)Mind Spike to remove any remaining ticks of any dots to maximize follow up Mind Blast, immediately hit Mind Blast
9) Revert to Phase One.
Is this completely wrong? A Spriest in 735 gear (I'm in 713) said I should never use any dots in single target dps (including Devouring Plague), which begs the question, why did she have SW: Insanity as a talent if you can't use it because you never apply Devouring Plague...
I feel like everything I thought I knew is wrong.
Just in case you need my stats:
32% Haste
57% Mastery
15% Multistrike
12% Crit
7% Versatility
EDIT: I should say I'm not particularly unhappy with my DPS, I do ~55k to ~65k with buffs, which is usually what I see from other shadow priests of the same gear level. I have no set bonuses or anything.