As far as setting CPU affinity, I've seen a marked improvement in my quad-core setup by NOT setting any wow instances to core 0; but spreading them out between the other cores. My focus window has affinity set to 1, the second and third instances are set to 2, and the fourth and fifth are set to 3. This allows all standard OS processes to run unhindered on core 0 and not cause hitching in the wow instances. With a dual core running 5 boxes, I'd put only 2 on core 0 and the other 3 on core 1. My two cents.