I am running 5 instances of WoW using HKN with the main toon on a 27" screen (2560X1440) and 4 clones on separate 24" screen (1920X1080). All 5 WoW windows are currently at 2560X1440 resolution (all under one directory). Frame rate is acceptable most of the time (around 60+ fps) but sometimes will drop to unplayable levels (below 10 fps) especially at crowed places (like Ashran).

Is there any way to boost the fps? I tried reducing resolution to 1920X1080 but resulting image on the 27" looks pretty bad. Text, for example, became way less sharp to the extend that they are difficult to read. Not sure if I am setting up WoW wrongly or problem lies with HKN. Suggestions?