FIGURED IT OUT!!

There was a driver from "New Software, Inc." for a product called "Folder-Lock", which is used to be able to assign a password to access windows folders, that was getting invoked by the Win7 System Kernel. I uninstalled this product, and presto, problem gone - no more 50% of CPU being used by system - - -

How I Did It::

I couldn't find any software or features within "Xperf", "Windows Process Monitor", or "Windows Process Explorer" that allowed me to "map" the offending Thread ID to the responsible driver. However, Windows Process Explorer does display info for all the Drivers being loaded/invoked for a given process - including the "System" kernel process.

So I just went and slowly browsed thru all 173 of them, and thought about what non-Microsoft drivers might possibly have something to do with locking up resources - a clue given to me by the Starting Address for the offending TID from Process Explorer:

"ntoskrnl.exe"!KeAcquireInStackQueuedSpinLockAtDcpLevel+0x1e0".

Normal "human heuristics logic" - - -