After googling around about my problems I've made two changes, the first one was to upgrade the controller firmware from 52.16.3-3913, dated April 2021, to the lastest one, 52.26.3-5250_A, dated December 2023.

Then, given several reports of HPE Gen10 units rebooting unexpectedly all suggesting to change the workload profile to max performance, I did this change to the BIOS, loosing SpeedStep, as it appears from /var/adm/messages.

Feb 20 09:20:33 pg-1 unix: [ID 950921 kern.info] cpu1: x86 (chipid 0x0 GenuineIntel A0671 family 6 model 167 step 1 clock 2807 MHz)
Feb 20 09:20:33 pg-1 unix: [ID 950921 kern.info] cpu1: Intel(r) Xeon(r) E-2314 CPU @ 2.80GHz
Feb 20 09:20:33 pg-1 unix: [ID 557947 kern.info] cpu1 initialization complete - online
Feb 20 09:20:33 pg-1 unix: [ID 977644 kern.info] NOTICE: cpu_acpi: _TSS package bad count 1 for CPU 2.
Feb 20 09:20:33 pg-1 unix: [ID 340435 kern.info] NOTICE: Support for CPU throttling is being disabled due to errors parsing ACPI T-state objects exported by BIOS.
Feb 20 09:20:33 pg-1 unix: [ID 950921 kern.info] cpu2: x86 (chipid 0x0 GenuineIntel A0671 family 6 model 167 step 1 clock 2807 MHz)
Feb 20 09:20:33 pg-1 unix: [ID 950921 kern.info] cpu2: Intel(r) Xeon(r) E-2314 CPU @ 2.80GHz
Feb 20 09:20:33 pg-1 unix: [ID 557947 kern.info] cpu2 initialization complete - online
Feb 20 09:20:33 pg-1 unix: [ID 977644 kern.info] NOTICE: cpu_acpi: _TSS package bad count 1 for CPU 3.
Feb 20 09:20:33 pg-1 unix: [ID 340435 kern.info] NOTICE: Support for CPU throttling is being disabled due to errors parsing ACPI T-state objects exported by BIOS.

Restarted iozone, let's see if something improves or not.

Regards.
Maurilio.