OK, I got Windows up and running, and everything appears to be normal. Since I had immediate issues running Folding@Home on Linux with all of the cores enabled, I threw that at it first. Absolutely no problem running on all cores. Resource manager shows every core using about 90% of available CPU power for each core.
I have several immediate observations. The CPU is running much cooler (~15-20°C) than it was under Linux. At the same time, running all out, the points per day metric from FAH was about 30% lower than it was under Linux. When checking the particulars of the client, I saw that it claims to be 32-bit code. I don't recall what it said for the Linux client, but perhaps the problem is running 64-bit code on that suspect core? ....