Deep Wound or quick-attack?

The MoD does give how long it took until death, in seconds, and I believe that takes into account deep wound. So you could try that.

Correct me if I'm wrong, but AFAIK Deep Wound damage caps at 100. Assuming that is the case.

Golden Fang Strikes damage(z) is: buffs + baseDMG + 100

Jagged Strikes damage is: buffs + baseDMG
Exhausting Assaults damage is: buffs*2 + baseDMG*2
Fox Fangs damage is: buffs + baseDMG + X

However, as you pointed out, GFS has a longer activation time. If we assume it takes twice as long to recharge we can use one of three combos in the time GFS takes to cast.

#1: JS + JS
#2: JS + FF
#3: JS + EA

#1's damage(y1): buffs*2 + baseDMG*2
#2's damage(y2): buffs*2 + baseDMG*2 + X
#3's damage(y3): buffs*3 + baseDMG*3

Looking at the above, whenever y1/2/3 exceeds z they are superior.

Assuming 13 dagger mastery, 16 SoH, 16 OoP. X = 32, buffs = (26 + 17).

y1 = 86 + baseDMG*2
y2 = 118 + baseDMG*2
y3 = 129 + baseDMG*3
z = 143 + baseDMG

When baseDMG ≥ 57, y1 is better then z.
When baseDMG ≥ 25, y2 is better then z.
When baseDMG ≥ 7, y3 is better then z.

baseDMG = the damage a single unbuffed hit does, on Cracked Armor.

Anyway, hope that answers your question.

Edit: Didn't account for baseDMG.

Really depends on whether or not the target lives past the second chain. In either scenario you will be cycling JS-FF-DB every other chain anyways due to recharges.

From that, it seems JS+JS doesn't exceed GFS (even with CA, dagger base damage won't be 57 or more in HM, probably not even in NM), and JS+FF doesn't really matter because the point of GFS is to use it during FF's recharge. EA is clearly better, but at 8r it won't be available during as many "FF still recharging" moments. GFS also can lead straight into another DB, which none of the other combos do (might not matter, but I don't know exactly how the attack speeds vs. recharges would play out).

JS = baseDMG + buffs
EA = baseDMG*2 + buffs*2
FF = baseDMG + buffs + X
GFS = baseDMG + buffs + DW
DB = baseDMG*2 + buffs*2 + Y*N

JS-EA-JS-FF-DB = baseDMG*7 + buffs*7 + X + Y*N

JS-GFS-DB-JS-FF-DB = baseDMG*8 + buffs*8 + X + (Y*N)*2 + DW

As you can see, the second one does somewhat higher damage even if we don't include Deep Wound. The thing is though that the second one takes 4.5s to finish, if we assume DB and GFS takes exactly one second and the rest take exactly half a second to activate, while the first one takes 3s. Keep in mind that EA has a fairly long cooldown and thus the first combo isn't really repeatable without modification, while the second one is almost completely repeatable (1s lag, assuming perfect timing) and does more total damage.

Edit: Fixed some errors.

Deepwound is used as much for the healing reduction as the max health reduction it causes. Over the entire duration of the enchantment it will either negate enough healing to be more worthwhile than another fast-dagger-attack or will force the enemy into expending energy to move it.

If you're a physical class with access to DW, you should ALWAYS bring it.

take deep wound, especially with the hm update coming later

Well, base damage will be a bit higher, so that puts even more favour in EA's court. I think, if you want a secondary attack it should be for utility; Brawling for KD or EA for rupt. The application of the maths may be largely irrelevant, unfortunately...