Grief...with or without Fort?

[the boss]

Pvp wise melee zeal duels(EXCLUDING smiters), do grief users really need fortitude to help them boost damage?
I could possibly sub-in duress in place of fortitude since damage difference in pvp is like...300-400 dmg lost?

How much do fort armors really help grief?

[jmsplat]

I believe duress is used mostly for the OW, and in zeal duels you hit often enough that it won't matter much