WoW defaults to utilize your two initial cores on a dual core machine (this may be different on dual core HT processors) please refer to the wow forums link below. They map out the wow setting for the processorAffinityMask variable and what you can set it to.

For just 3 instances on a dual core, I'm not sure that there is probably much reason to split it up any differently. Maybe have your primary run on your second, since I believe most of the OS and other apps will run off of the first core. Other then that, I'd say it probably won't make to much of a difference.

[Keyclone] Keyclone on 5-boxes : recommended CPU Affinity ?

http://forums.worldofwarcraft.com/th...78017311&sid=1