This is a very simple optimization that some people don't know about. There are two ways to go about this. You can go into your World of Warcraft folder and find the folder labeled [W T F]. Inside that folder you will see a file called [config]. Open that file with [WordPad]. Scroll to the very bottom of the file and type this in on a new line [SET processAffinityMask "'48"]. Make sure when you close the window you select [Save] changes. The other way is to simply log into your character and in the chat box type in [/console processAffinityMask 48]. Both ways have the same result. What you are doing when you set this is making World of Warcraft run on your CPU's Core 5 and Core 6 leaving Core 1 - 4 unused for Windows based tasks and other programs.
Hope this is useful to anyone playing World of Warcraft with an AMD Phenom II x6.
P.S. if you are using a AMD Phenom II x4 and you want wow to run on Core 3 and 4 leaving Core 1 and 2 open you simply change the number to 12 so it looks like this [SET processAffinityMask "12"] or [/console processAffinityMask 12]
KEEP IN MIND. You do not insert the [ ] when you type in the info.
Another thing I remembered is if you are using Windows 7 32-bit and/or 64-bit, there is a new feature implemented into the OS called [Core Parking], it is not ideal for playing video games and I would Google it and learn more about it for yourself. I did and I ultimately ended up disabling it.
GL everyone and good gaming!
Case: Lian Li X900B Mid Tower MB: ASUS Crosshair IV Formula CPU: AMD Phenom II x6 1090T Heatsink: Corsair H50 GPU: ASUS Matrix ROG Radeon HD5870 RAM: Corsair Dominator 4GB DDR3 SSD: Intel 160GB HDD: WD VelociRaptor Monitor: ASUS 23" HDMI PSU: Corsair Pro Series AX850 OS: Windows 7 Ultimate 64bit