Threading Changes
Following is the DEFAULT settings Skyrim uses:
iNumHWThreads=4
iHWThread6=5
iHWThread5=5
iHWThread4=5
iHWThread3=4
iHWThread2=4
iHWThread1=4
iAIThread2HWThread=5
iAIThread1HWThread=3
iRenderingThread2HWThread=1
iRenderingThread1HWThread=0
Here's the simple truth. If you have 4 cores, or 2 cores, don't change this. Just don't. Remove it from your INI file if you have.
Skyrim by default uses 4 cores of your CPU (iNumHWThreads=4). These cores/threads are each allocated to different tasks. The variables are perfectly set to leave room for different tasks by default. For example, notice the gap between Rendering and AI, there is one thread free. This is used for the audio thread. There is a gap between the AI threads too, used for 3 of the HWThread's. 5 is shared with AI Thread 2. This is a wildcard of sorts. This works for 4 cores, and should be left alone.
If you have 8 cores however (Hyperthreaded too if you're brave), you have the option of moving the work of iHWThread4, 5 and 6 to a separate core from iAIThread2HWThread, and telling Skyrim that you have 8 cores, not 4.
Add these if you have 8 cores.
iHWThread6=6
iHWThread5=6
iHWThread4=6
iNumHWThreads=8