something is telling me you have all the settings maxed out, FXAA, physics and shadows and full world spell effects.
ive got a more powerful system then that, in order for me to maintain 60 FPS running around anywhere, i need to adjust shadows, physics quite the well down, and i dont need FXAA on, looks good enough without it, also have other spell effects off, if people are doing fate zergs with 300 people, thats very intense no matter the system.
take of limb darkening as well, the game looks better without it imo, and motion blur i hate anyways in any game so i take that off
a svara zerg, with those settings adjusted, i get 40-45 fps sustained, which is very good when you consider how many people are there.
the 24 man raids arent released so there isnt a consistent measure of FPS yet.