In short for summary our 8 series motherboard can support C6/C7 with supported PSU and CPU.
It needs Intel utility (C–State Residency Monitor), with this utility installed we can monitor CPU C-state in Windows Performance Monitor.
But the utility is Intel confidential for vendors, so we cannot offer it if user want to test he may need find it from internet or somewhere.
Please refer the attached pictures for the test of C7 state and Package C7 state with dual monitor and single monitor.
There are some hint of the C state test.
#1 Want to test C6 state need to disable C3 and C7 first, if C7 is enable system will enter C7 directly not enter C6.
#2 With C3 disable and C6, C7 enable in the Windows Performance Monitor still can see C3 is working, it’s Haswell normal behavior.
Below picture is the BIOS setting for testing C7 state.
The test process is same for Package C3,C6 state.
For Package C7, need change some setting of power plan as below picture (turn off the display in specific minute)
After system turn off monitor automatically, move mouse let the screen back can see system has been enter Package C7 state in the Windows Performance Monitor.
If system cannot enter Package C7 successfully , please check [SATA Aggressive Link Power Management] option is enabled.