Hi there,
I was about to ask the exact same question that JeffSuperb had already asked here.
I find the answer to be missing the point of the question.
Jeff and I are not trying to find the current read/write speed of the disks, but instead trying to find the "active time" (referring to jeffs windows task manager picture).
If the active time is 100%, we know that the HDD in question is working as fast as it can.
This would help identify SMR disk write problems or multidisk operation bottlenecks.