I was sternly lectured in another thread that Linpack is limited to one thread per core. There are links that report the results of testing, where multi-threading usually slowed processes down.
I started that thread because when I ran Linpack 11.0.5.009 with its batch file, it ran at 100 Gflops (default cpu speed). LinX with Linpack 11.0.5.009 ran one rep at 160Gflops, then stopped on error.
Watching in real time with TMonitor I could see Linpack stop using half the threads during the middle of a run. When I disabled hyperthreading, the Gflops on the default speed rose to 189 Gflops.
When I ran normal LinX (presumably pre-Linpack 10; no AVX) I was able to OC the chip to 4.7 GHz. When I ran LinX with Linpack 10 (has AVX), I had to back off the OC, down to 4.4-4.5 GHz. With Linpack 11 (AVX2), I'm down to 4.3 GHz.
Since the HT issue is a Linpack problem, I can turn HT back on for normal use.