Well, SpeedStep has never been perfect and never will be
There are too many variables that can cause speedstep to never down the Core Voltage and Frequency
In some cases it can actually work backwards and never step back up when needed.
Personally, if there is ever a chance for me to turn it off I do. I set sleep modes instead.
Enhanced Intel SpeedStep® Technology - How To Document
Please Note:
To verify that Enhanced Intel SpeedStep Technology is enabled, do the following:
Close all applications and ensure that Windows OS is in idle mode.
(Note from me: Rarely will this ever be achievable, Too many things running in the background to achieve this level)
Press Ctrl + Alt + Delete and select the "Performance" tab.
Verify that CPU usage is 0. (This is almost impossible on todays PC's, see above)
Right click "My Computer" and select, "Properties."
Under the "General" tab, examine the installed processor and speed.
If Enhanced Intel SpeedStep Technology is enabled, two processor speeds will be listed.
The first speed listed is the specified speed of the processor.
The second speed is the current operating speed.
The second speed will be less then the first speed. (See Figure 1.)
This indicates that Enhanced Intel SpeedStep Technology
has effectively lowered the processor voltage and core frequency, which can (depending on system usage and design)
result in decreased average power consumption and decreased average heat production.
If Enhanced Intel SpeedStep Technology is off, then both processor speeds will be equal. (See Figure 2.)
If the processor is not in idle mode, Enhanced Intel SpeedStep Technology can be enabled and both processors speeds can be equal. If this happens, try steps 1-3 again.