After several fruitless hours trying to figure out how the hell to model an optimal damage cycle for a new shadow priest, I figured I would come pose the problem here. In general, there are just too many variables. With Vampiric Embrace and Vampiric Touch always up, there are infinite ways to arrange other spells in the gaps. The fact that Mind Blast can have six different cooldowns makes me want to shoot myself, because every half a second you shave off alters whatever model you were working with completely. Simple questions like "which is better, one point in improved mind blast or one point in shadow power?" are actually absurdly complex, because you can't compare the talents in a meaningful way until you find the optimal damage cycle for each talent build. Throw in downranking, damage dealt to oneself with Shadow Word: Death, the problem of scalability . . . ugh. I really hope that someone has the know-how to code something to find a solution to this particular problem.

Basic assumptions:

(1) You have exactly 700 +dmg, 200 spirit, 6% crit, and 0 mana/5
(2) To simplify things, your spells are never resisted
(3) You're level 70, and have access to all ranks of Mind Flay, Mind Blast, Shadow Word: Pain, Shadow Word: Death, Vampiric Touch, as well as Vampiric Embrace . . . but nothing else. No other spells or augmentations from either the priest (except for talents), any other class, or items are assumed
(4) Vampiric Embrace and Vampiric Touch need to be up at all times
(5) To simplify things, assume five stacks of Shadow Weaving are up at all times, including at the start of the cycle
(6) You have spent 10 points in discipline and 41 points in shadow, yielding a damage modifier of 152.75% as such: http://www.worldofwarcraft.com/info/...10251123051051. Ten talent points are up in the air

Basic questions:

(1) With additional talents, what's the damage cycle with the most dps?
(2) With additional talents, what's the damage cycle that scales the best (that is, gains the most benefit from +1 spell damage)?
(3) With additional talents, what's the damage cycle that yields the highest dps while spending 0 mana per second (i.e., indefinitely sustainable)?
How about spending no more than 20 mana per second? 40? 60?
(4) With additional talents, what's the most efficient damage cycle which outputs at least 95% of the dps of the highest-dps damage cycle? 90%? 85%?

Again, these questions are beyond my ability to answer, and I would appreciate it greatly if someone who knows how to crunch the numbers would take a stab at them.

Hmm. This is tricky. I'm currently checking some possible combinations, but the start is tricky, as well as having to keep both DoTs up.

Start:
00.00s Vampiric Touch Start
01.50s Vampiric Touch Cast
01.50s Shadow Word: Pain
03.00s Vampiric Embrace
04.50s Shadow Word: Death
06.00s Mind Flay Start
09.00s Mind Flay End
09.00s Mind Blast Start
10.50s Mind Blast Cast
10.50s Shadow Word: Death
12.00s Mind Flay Start
15.00s Mind Flay End
15.00s Vampiric Touch Start
16.50s Vampiric Touch Cast
16.50s Mind Blast Start
18.00s Mind Blast Cast
18.00s Shadow Word: Death
19.50s Mind Flay Start
22.50s Mind Flay End
22.50s Mind Flay Start
25.50s Mind Flay End
25.50s Shadow Word: Death
27.00s Mind Flay Start
30.00s Mind Flay End

Damage numbers (assuming full shadow weaving, etc., like the original poster specified):
Shadow Word: Pain = 3160 over 24 seconds, or 395/tick.
Mind Blast = 1238 Average.
Mind Flay = 1255 over 3 seconds. 418/tick.
Vampiric Touch = 2119 over 15 seconds, or 423/tick.
Shadow Word: Death = 1393 average.
I can't find anywhere with proper numbers on the strength of the new ranks of Mind Blast and Shadow Word: Pain, so I've assumed the highest level non-expansion version of both.

The above cycle contains:
9 ticks of Shadow Word: Pain and Vampiric Touch.
4 Shadow Word: Deaths
2 Mind Blasts
5 Mind Flays
This is 21685 damage average, or 722 DPS. And I bet it's not even optimal; an optimal cycle would probably fit in some more Mind Blasts. I don't think it's possible to figure out a repeating cycle which is shorter than a few minutes however.

The mind blast cooldown starts once the spell is actually cast, so with the 1.5 second cast time, you can cast it once every 9.5s untalented, or 7s talented, which prevents a simple 6s cycle.

personally i would use this build for raid dps:
http://www.worldofwarcraft.com/info/...10250123051551

notable changes:
- drop imp fear and silence. neither will be more than an occasional help in raids. not at all worth 3 points that can be picked up else wear
- grab meditation(3/3) and innerfocus for better mana longevity.
- drop shadow focus to just 2/5 and grab 5/5 shadow power
- 4/5 imp mind blast. mindblast, mindflay, mindflay, mindflay and the mindblast is off cooldown. 5/5 mind blast is a waste because the extra 0.5 second comes up while mid mindflay.
- the last point i put in mental agility, which decreases your instant casts mana cost by 2%. this might not be worth it as there aren't a ton of instant casts. perhaps put that back into shadow focus for another 2% chance to hit.

Good luck.

The release of the alpha completely killed my willingness to do this math, but I salute you and wish you the best. It's absurdly more complex because of cooldowns.

When I was working it out for a level 60 priest, I went far enough to determine the order in which you would rank up spells, but that's all thrown out with the changes to downranking etc. As a starting point, you will always want SW:Pain up, as it is the single largest damage per 1.5second global cooldown available. Then you have to look at mind flay vs mind blast - you don't just jump up to max rank blast, you swap back and forth between flay/blast in ranking up.

As I said at the top, good luck =P

The problem isn't as easy as "spend four points in improved Mind Blast so you can cast Mind Blast once every 7.5 seconds". Pretty much no matter how you set things up, you can never cast Blast/Shadow Word: Death each and every time they are on cooldown. You miss a lot of casts. Take, for example, this sketch of a 2-minute cycle. The only things we're doing here are trying to keep VE, VT, and SW:P up at all times:

0.0: Vampiric Touch
1.5: Shadow Word: Pain
3.0: Vampiric Embrace
(10.5 seconds)
15.0: Vampiric Touch
(9 seconds)
25.5: Shadow Word: Pain
(3 seconds)
30.0: Vampiric Touch
(13.5 seconds)
45.0: Vampiric Touch
(3 seconds)
49.5: Shadow Word: Pain
(9 seconds)
60.0: Vampiric Touch
(1.5 seconds)
63.0: Vampiric Embrace
(9 seconds)
73.5: Shadow Word: Pain
75.0: Vampiric Touch
(13.5 seconds)
90.0: Vampiric Touch
(6 seconds)
97.5: Shadow Word: Pain
(6 seconds)
105.0: Vampiric Touch

The gaps between the critical spells are what you have to work with, and they constrict you in a meaningful way. In every gap that's not a multiple of three seconds, you should be casting either SW:D or Mind Blast. If you just do that, though, you're left with a lot more Mind Flays than you need. Basically, you want to squeeze as many Blasts and Deaths into a cycle like this as possible. Some changes in MB cooldown help your cycle a lot, and some don't. The problem is decidedly nontrivial.

As far as new spell ranks, here are the maximum ranks of each of the relevant spells:

Shadow Word: Pain rank 10 - 575 mana, 1236 damage over 18 seconds
Vampiric Touch rank 3 - 475 mana, 687.5 damage over 15 seconds
Mind Blast rank 11 - 450 mana for 728 damage
Shadow Word: Death rank 2 - 309 mana for 618 damage
Mind Flay rank 7 - 230 mana for 528 damage

Of course, downranking might be optimal, especially in the case of Vampiric Touch.