My previous power draw tests were with the BIOS setting for Server / Power Management set to "Node Management". I changed this to "OS Control/EIST" on both nodes and checked "idle" power, and again measured about 240W. So no change between those 2 settings that I could tell.I have a feeling there is something in the BIOS that we are missing.
The other 2 choices are "Max Performance" and "Active Power Controller", both of which disable Speedstep.
I tried the "Active Power Controller" setting just to see how it effects things. Once both nodes were idle in Server 2012, the power draw didn't seem to be much different ... maybe a handful of Watts at best ?
So I don't see any effect on idle power draw from BIOS settings. Maybe it's a Linux / Windows thing ?