If you find that when you encounter a World Boss with a gazillion other players, and are experiencing enough lag to insulate your loft space then try this small adjustment.
Hit the 'esc' key until your menu appears, then select "Video "Options",and then the "Advanced" tab.
About half way down, find "Particles", and untick "Enable World Particles", and adjust "Limit Spell Particle Effects To" to "Don't Show Anything".
Further down, near the bottom, find the "View Ranges" and adjust the slider for "High Quality View Distance" from its usual 75% down to 0%.
Then click on OK and "Resume Game". You might find the sound which accompanies spells & casting is muted.
This only takes a moment to do, and is easy enough to reverse when you want to go back to questing / grinding.
This adjustment may not be quite as pretty on the eye, but it may help with the massive lag people are experiencing.
Hope this works as well for you as it did for me.