I still have some time to test - let me try this out! One thing I already proved is with 2GB ram, the system performs as predicted ~20 GB/s. But, I resonate with your definition of benchmarking - to test utlimate performance but also real world usage.

Update:

Ok, so I used the ':' syntax in the --filename option, I got something that makes sense. FIO created invidual files for each thread. I test numjobs: 4, 8, 16 and it plateaus around 8 jobs. Adding additional files+jobs actually makes things worse.

  neil@ubuntu:~/mnt/disk$ ls
  dummy0  dummy10  dummy12  dummy14  dummy2  dummy4  dummy6  dummy8
  dummy1  dummy11  dummy13  dummy15  dummy3  dummy5  dummy7  dummy9
  neil@ubuntu:~/mnt/disk$ sudo fio --name=read_test \
  >         --filename=/home/neil/mnt/disk/dummy0:/home/neil/mnt/disk/dummy1:/home/neil/mnt/disk/dummy2:/home/neil/mnt/disk/dummy3:/home/neil/mnt/disk/dummy4:/home/neil/mnt/disk/dummy5:/home/neil/mnt/disk/dummy6:/home/neil/mnt/disk/dummy7:/home/neil/mnt/disk/dummy8:/home/neil/mnt/disk/dummy9:/home/neil/mnt/disk/dummy10:/home/neil/mnt/disk/dummy11:/home/neil/mnt/disk/dummy12:/home/neil/mnt/disk/dummy13:/home/neil/mnt/disk/dummy14:/home/neil/mnt/disk/dummy15 \
  >         --filesize=20G \
  >         --ioengine=libaio \
  >         --direct=1 \
  >         --sync=1 \
  >         --bs=512k \
  >         --iodepth=1 \
  >         --rw=read \
  >         --numjobs=16 \
  >         --group_reporting

I get around ~22GB/s with 8 jobs, ~15 GB/s with 16 jobs. Thanks for correcting, I'll post an update to the misleading 157 Gb/s... uff.

Updated the article: https://neil.computer/notes/zfs-raidz2/#note-5