I turned off displaying effects. In my case it was because having the whole screen filled with flashing flaming effects was blocking my view of where characters and mobs were and which of them was selected (since with default settings this game is too flashy for good visibility), but it should help with lag issues as well.
I doubt things like turning off display of headgear and sheathed weapons would have an effect, though. For one thing that only affects how your own character is displayed, not anyone else's, and your weapon won't be sheathed during these crowded fates anyway, so the difference is just a single character's helmet.