Jairek

Eviscerate is not the best example, as stated, so it's best to include variations for Sinister Strike and Backstab. There are also other variables that will affect the value of Mongoose vs. Executioner, like the Relentless Earthstorm diamond.

All PvE combat builds from here on will likely include Aggression, so it should be included as a multiplier as well.

For Sinister Strike (20/41):
SS = wpn + 98 + ((AP / 14) * 2.4)
damage = SS * (1-armor_mitigation) * 1.06 * (2.3 * crit + (1-crit))

For Backstab (15/41/5):
BS = 1.5 * (wpn + ((AP/14) * 1.7)) + 255
damage = BS * (1-armor_mitigation) * 1.26 * (2.24 * (crit + .35) + (1 - (crit + .35)))


In the case of Mongoose + ToA / FoV, 1720 base AP, 24% crit rate:
armor_mitigation = .17179 or (2190 / (2190 + 10557.5))
SS = 260.5 + 98 + (((1720 + 120) / 14) * 2.4) = 673.93
ss_damage = 673.93 * .82821 * 1.06 * (2.3 * .27 + (1-.27)) = 799.31

BS = 1.5 * (252.5 + (((1720 + 120)/14) * 1.7)) + 255 = 968.89
bs_damage = 968.89 * .82821 * 1.26 * (2.24 * (.27 + .35) + (1 - (.27 + .35))) = 1788.40


In the case of Executioner + ToA / FoV, 1720 base AP, 24% crit rate:
armor_mitigation = .11337 or ( (2190-840) / (2190-840 + 10557.5) )
SS = 260.5 + 98 + 1720/14*2.4 = 653.36
ss_damage = 653.36 * .88663 * 1.06 * (2.3 * .24 + (1-.24)) = 805.63

BS = 1.5 * (252.5 + 1720/14*1.7) * + 255 = 947.04
bs_damage = 947.04 * .88663 * 1.26 * (2.24 * (.24 + .35) + (1 - (.24 + .35))) = 1832.22


So, by comparing:
SS w/ mongoose = 799.31
SS w/ executioner = 805.63
BS w/ mongoose = 1788.40
BS w/ executioner = 1541.22

The damage difference on Sinister Strike is fairly negligible, but is a bit more substantial for backstab.

When it comes to white damage, executioner should come out ahead. The rogue specials have far more multipliers when it comes to critical strike damage, which do not translate to white damage.

This also only applies to the damage of the two specials that occur within the duration of the buff itself. It also only applies to a boss like Vashj, and not a more heavily armored one like Void Reaver. It seems to me that Mongoose holds more "general" utility for a rogue, while Executioner will grant fair dps gains for encounters where a boss's armor is not incredibly large.