What is the closest equivalent of "load average" in Windows available via WMI?

The Process Queue Length count from the System performance counter object is:

Processor Queue Length is the number of threads in the processor queue[...]

This value is available in WMI via Win32_PerfFormattedData_PerfOS_System.

I don't know of any such measure of overall work-demand, it's just percent-CPU with some breakdown in the kinds of CPU demanded. This does make it hard to figure out just how overloaded a machine is. When a Linux system is reporting a Load Average of 63 and the Windows system is reporting 100% CPU... well, they're both running flat out, but that's about all you can tell about the Windows system.

I'm not sure that there is anything in windows that would be equivalent, and I'm not sure it would mean anything if there were there. From the description I can't see how a process would fail to be included as even a hung or suspended process would get CPU time allocated. Additionally it's more relevant to look at threads and runnable threads rather than processes under windows in order to determine any notion of load by the definition provided.