It was 660 or something like that. If you have 100% life leech in dest, that's 6.6 life per hit, but doesn't work against heroic shields like life on striking. If your weapon damage average was 2k, that'd be like 30 EWD = 75 str using a necro scythe. If you rolled 70 max damage on your amu, it would beat doom with 2k ewd, as would 40 str with 100% bonus to str. Actually you could beat it with less since parasite has 5/4 wdm which multiplies max damage and str, but not the flat damage from doom.
Also ttad doesn't work with projectiles (from what I've tested, unless throwing weapons are an exception), so you're better off with a +5 amu and 400 life. If you want a proc, the best is banish because it deals like 40-50k "damage" to dunc/fauzt mobs (you'd need to hit a doomed mob ~75 times to do that kind of damage).
According to docs the -magic resist on doom doesn't work without a hard point, but this is something that would have to be confirmed by using a maphack, since many things don't work how they're supposed to.
Overall doom is shitty unless you multihit alot and have a low wdm modifier (tantrum, wychwind, whirlpool etc).
As for merc, you can't go wrong with A5 merc since you can gear them up depending on what you want.
Nagibarb - eth TalXis flamberge + strength beyond strength and full STR stack = easy 80k AOE damage. A5 mercs can actually solo bremmtown with shit like SSU flamberge, just stand back and cast erydem. Razorspine would be another interesting armor choice. Eth esubane with kab runes could also be godly.
SU crystal sword + hellmaw + lite spell stack - should 1hk any non lite immune mob (necrobots) since supernova has no nd. Could also try SU claymore + SSU avenger guard.
Cheapo meatshield generator - stack as much reanimates as possible. You can get 5% reanimate destroyer shaman on rare amulets/gloves. Stack KO runes for extra damage.
Fusion generator - Mal belt + zod barb helm + fire spell stack, punish those necrobots.
Buffbot - SSU giant sword + T6 scale mail for +578 EWD / +191 ele damage / +83 phys-magic. Use NIH runes / SU greaves / niradyahk to boost motw duration.
Crowd control - DW set armor or SU field plate + SSU full helm + SSU great sword + community belt + nightmare amu.
Highly theoretical - Gilgamesh RW MOed with spike nova + razorspine + auhe belt + stormblast gloves + SSU horned helm, searing glow should off somewhat nicely in a place like fauzt.
Mount Arreat set armor/helm/gloves - 25% ctc L8 guard tower when you kill an enemy.
Wold dudu set armor/belt - 60% str + 200 str + 100 EWD + 10% ctc bladestorm = godly. These two items alone probably add like 1k EWD to your merc. Could be done with creepy crafts while losing proc.
Etc...
Keep in mind 1 str = 1 EWD. So 5k str on A5 merc means x51 damage multiplier.