1 mil crit damage is pretty normal now.
Many skills can deliver more than 1million crt dmg, in the range of 1-5 million crit damage, such as firebats, HOTA, Bola, spike trap, Wave of light, Zombie Charger, meteor etc.

If my memory serves me right, Sever deliver more than 10 million of damage in final blow.

Sever is an awesome weapon @ low MP (MP8 and below), where you can kill mobs in 1-2 hits.

Honestly speaking, both of them are not good for high MP because the damage is too low.
Both of them should not be the option if you want to push your DPS more than 250K.

Please give your profile link.
Are you playing monk? If you want to have cheaper option, try skorn.
To use skorn, you need to stack some IAS gears.
You need to spend some gold to buy decent weapon. That's for sure.

Based on current 200K+ DPS build, generally you need to have 2500-3000 DEX / 50% CC / 500% CD / 60%+ Attack Speed (dual-wield).

Yes, try achieve those specs.
60% attack speed if you dual-wield.
-15% if you use 2H weapon like skorn.

Dual wield gives you additional 15% attack speed by default.

Make it simple, try to have 45% attack speed (i.e. +9% IAS from 5 gears).

If you can stack more than 45% attack speed, by all means please do so.
The more the merrier.

Forgot to tell you, do not just push the DPS.

Make sure you have adequate EHP too.
500K would be good. 600K would be quite solid. The more the merrier.

If you use skorn, try look for skorn with at least 5% LS.

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