On a one-minute single-boss fight the build is Tuned 17/3/31 · 1 min, 17/3/31. It spends 31 points in Subtlety to reach 
Hemorrhage and 
Thousand Cuts, and 20 in Assassination for 
Relentless Strikes, 
Ruthlessness and 
Malice on the way to 
Cold Blood.
0/3
0/2
0/2
0/2
0/5
0/2
0/1
0/2
0/5
0/1
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0/3
0/3
0/3
0/2
0/1
0/2
0/2
0/1
0/5
0/1
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1/3
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1/1
0/5005303103011-3-0321203310213211501Every fight and faction has a build of its own, searched by simulation. They differ only in the filler and in where three or four cheap points go, and what follows applies to each.
Why these talents
Hemorrhage is your builder, and without it the build loses 60.0 % of its damage. For 35 Energy it deals 100 % weapon damage (145 % with a dagger), awards a combo point and leaves a 15-second debuff that makes the target take 15 % more from your Rupture. Its damage is normalized: your attack power counts at a fixed 2.4-second speed for a one-hander and 1.7 for a dagger, which is what the dagger's higher percentage makes up for.
Relentless Strikes refunds 25 Energy, with a 20 % chance for each combo point a finisher spends. One point is worth 7.4 %, more than any other talent but Hemorrhage, because every finisher rolls it, and you cast about 3.2 Ruptures and 3.1 Slice and Dice a minute.
Ruthlessness: after any finisher, a 60 % chance of one combo point back, worth 4.7 %. It is why a short Slice and Dice is the right refresh here: more often than not the point comes straight back.
Thousand Cuts is the 31-point talent. Each Rupture tick, every 2 seconds, takes 3 Energy off your next Hemorrhage, up to 15, for 10 seconds. It is worth 3.6 %, and the discount is up 42.5 % of the fight. It is also why the searched rotation puts Rupture back on the boss as soon as you have three combo points: every second without Rupture is a second without the discount.
Serrated Blades strips 9 % of the boss's armor from all your attacks and adds 30 % to Rupture, worth 3.0 %. Forever changed the armor part from a flat amount to a percentage. You need all three points for Hemorrhage anyway.
Malice is 5 % crit, now for your poisons as well as your attacks, worth 4.0 %. 
Improved Slice and Dice stretches Slice and Dice by 45 %, so a one-point cast lasts 13 seconds. It is worth 5.4 %.
Flexible points
- The filler in Subtlety. Camouflage, Master of Deception, Opportunity, Improved Ambush, Initiative, Setup, Elusiveness and Heightened Senses are worth nothing in a boss fight. The rotation never casts Ambush, Backstab, Garrote or Cheap Shot, can't use Stealth in combat and is never the boss's target. They are the 16 points you pay to reach Thousand Cuts. Spend them on utility:
Elusiveness at 2/2 brings Vanish back after three and a half minutes, which only a longer fight than ours rewards. 
Dirty Deeds does nothing here either, but 
Quietus requires it, and Quietus is worth 0.6 %: 10 % more Hemorrhage damage once the boss is below 35 %.
- Improved Poisons. On one-minute fights the build keeps a single point of
Improved Poisons and puts the other three into Improved Eviscerate (see the last section).
Lethality is in the build because Cold Blood needs 15 points above it, and nothing else in those rows adds damage in our fights. Three points are worth 0.6 %.
Ghostly Strike is a point on the way down the tree. It is worth 0.4 %, inside the noise, because the rotation rarely has 40 Energy when Hemorrhage is cheaper.
What each talent is worth
Each number is the build simulated again with that talent removed, so the values overlap and won't sum to your total. The last-point column is the cost of removing a single point, the one to read when a spare point is looking for a home.
On every fight
The one-minute builds move three points from Improved Poisons into 
Improved Eviscerate, the first Combat talent, for 20 % more Eviscerate. On a short fight the opener's Cold Blood Eviscerates are a bigger share of your damage, and the swap is worth 1.6 % there. Cold Blood, Premeditation and Preparation all climb on one-minute fights for the same reason: Cold Blood is worth 3.1 % there. The other moves only swap one kind of filler for another. The table compares each fight's build with this one.