For those who use Hotkeynet, the following post applies:

Quote Originally Posted by 'Freddie',index.php?page=Thread&postID=180029#post 180029
Quote Originally Posted by 'Owltoid',index.php?page=Thread&postID=179776#post 179776
Eight processors are shown and the first two out of the eight were at full utilization while the other 6 looked low (under 25%).
That's a picture of what Memn described in words. By default, WoW restricts itself to the first two cores, so all five WoW instances are running to full capacity on just those two cores and bottlenecking. Meanwhile the other six cores have practically nothing to do. It's sort of like driving a Ferrari with the pedal to the floor, but with most of the spark plugs disconnected.

This default setting (which is programmed deliberately by Blizzard) is horrible. The only way you could invent a worse setting would be to restrict all your WoWs to one core. I agree with Memn that the best thing you can do right now is set every WoW to run on all eight cores. That will be pretty close to optimal because (like Memn says) it gives maximum latitude to the operating system's thread scheduler to optimize things. Later if you want you can experiment and fine tune it.

If you choose to set your affinity that way, the HotkeyNet command (for each window) is

Code:
<SetAffinity all>
It was extremely quick and easy. Just paste the command <SetAffinityAll> after your command to open an instance of WoW and you're all set.