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Overview Edit

In the following theoretical calculation Mutilate Rank 4 is compared to Backstab Rank 10. The rogue is assumed to have full Seal Fate, Opportunity, Improved Backstab and Mutilate for comparison purposes.
The [Gladiator's Shanker] is used in the main and offhand.
The Rogue is assumed to have a 25% base Critical chance including talents and 1400 Attack Power.
The imagined victim is assumed to have no Mitigation at all and is also assumed to be poisoned all the time.
Both Backstab and Mutilate cost the same amount of energy but if glyphed Mutilate will cost a bit less energy.

Calculation Edit

Definitions Edit

Critical Strike Chance: Crit = 25% = 0.25
Backstab Critical Chance: BSCrit = 25% + 30% = 55% = 0.55

Attack power: AP = 1400

Average weapon damage: AWD = (131 + 197) / 2 = 164
Attack Power modifier: APM = 1400 / 14 * 1.7 = 170

Weapon Damage: WD = AWD + APM = 334

Opportunity multiplier: Opp = 1 + (0.04 * 5) = 1.2

Offhand Weapon Damage Penalty: OffPen = 0.5 + (0.05 * Dual Wield Specialization Rank) = 0.5 + (0.05 * 0) = 0.5

Critical Strike Damage Multiplier: CritMult = 2 + (0.06 * 5) = 2.3

Poison Multiplier: Pois = 1.5

Mutilate Damage Edit

Base Mainhand Damage: BMHD =  WD + 101 = 435

Mainhand Damage = BMHD * Pois * Opp = 435 * 1.2 * 1.5 = 783
Mainhand Critical Damage = 783 * CritMult = 783 * 2.3 = 1800.9

Base Offhand Damage: BOHD = WD * OffPen + 101 * (1 + 0.1* Dual Wield Specialization Rank) = 334* 0.5 + 101 * 1 = 268

Offhand Damage  = BOHD * Pois * Opp = 268 * 1.2 * 1.5 = 482.4
Offhand Critical Damage =  482 * CritMult = 482.4 * 2.3 = 1109.5

Chance For Each Possible Event:

Event 1: Mainhand Doesn't Crit AND Offhand Doesn't Crit = 0.75 * 0.75 = 0.5625
Event 2: Mainhand Crits And Offhand Doesn't Crit = 0.25 * 0.75 = 0.1875
Event 3: Mainhand Doesn't Crit and Offhand Crits = 0.75 * 0.25 = 0.1875
Event 4: Mainhand Crits and Offhand Crits = 0.25 * 0.25 = 0.0625

Damage For Event 1: 783 + 482.4 = 1265.4
Damage For Event 2: 1800.9 + 482.4 = 2283.3
Damage For Event 3: 783 + 1109.5 = 1892.5
Damage For Event 4: 1800.9 + 1109.5 = 2910.4

Average Mutilate Damage: 0.5625 * 1265 + 0.1875 * 2282.9 + 0.1875 * 1892.5 + 0.0625 * 2910.4 = 1676.65

Backstab Damage Edit

Non-Critical Damage = Opp * ((WD) * 1.5 + 255 ) = 1.2 * ((334) * 1.5 + 255) = 907.2
Critical Damage = 907.2 * 2.3 = 2086.6

Average Backstab Damage = 907.2 * (1 - BSCrit) + 2086.6 * (BSCrit) = 1555.8

Simulation Edit

Lets assume that the rogue hits his target 100 times with Mutilate and 100 times with Backstab.

Mutilate Edit

Even if both weapons crit, only one extra Combo point is generated.
Total Damage = 1676.65 * 100 = 167,665

Combo points gained: 100 * (CP From Mutilate) + 100 * % of Events With A Single Crit  
  = 100 * 2 + 100 * (.1875 + .1875 + .0625) = 243.75 = 243

Backstab Edit

Total Damage = 1555.8 * 100 = 155,580 

Combo points gained: 100 * (CP From Backstab) + 100 * BSCrit = 100 * 1 + 100 * .55 = 155

Summary Edit

In 100 attacks:
Mutilate does 167,665 damage to the target and grants 243 Combo points.
Backstab does 155,580 damage to the target and grants 155 Combo points.

NOTE1: The above calculations do not include many talents, notably combat potency, surprise attacks, and relentless strikes.

NOTE2: The above calculations were written by someone that favors mutilate. The main issue would be what spec you would go to maximize backstab (full sub). I would like the original author to reproduce the calculations with the favorable talents included for backstab(20/0/41). The attack power and agility are both increased in sub, as well as 10% bonus to backstab, making crit and dps both higher on the base for backstab to compute these calculations. The difference of 8% that is achieved by these calculations lacking the 10% to AP, 15% to agi, 10% to backstab would clearly be over matched when added in, but then what does the effect of seal fate have on the calculations.

NOTE3: While it is true an all-out subtlety spec would increase the damage of backstab itself, the above calculations also fail to take into account a spec that is designed to optimize total damage output utilizing mutilate. Such a spec includes dual-wield specialization in the Combat tree, not only for its increase to Mutilate but for its increase to white damage as well. In short, for a raw comparison of the two abilities themselves in a situation where they're on approximately even footing, the above calculations are reasonably accurate (theory can only go so far.)