So the question is: does +4 to assassinate on Dark Diversion and +2 on EMG stack?
My guess is that it doesn't (would be too good) but i don't know.
The other question now is for thunder forged weapons.
Both dagger and kukri have same base dmg (1d4) and with improved critical and knife specialization:
TF dagger: 15-20 x3
TF kukri: 12-20 x3
if I'm not mistaking.
Now, because I prefer to have only one improved critical feat, and Agony is already keen, do you see any reason to go for daggers?