I would be interested to make that measure as well.
So far I have found this benchmark: https://storage.jamesachambers.com/ with simple command to run. Unfortunately I think it will not run from HassOS. For test to make RPi needs to be booted up with “normal” linux OS.
# dd if=/dev/zero of=/mnt/data/temp.img bs=8k count=256k
262144+0 records in
262144+0 records out
2147483648 bytes (2.0GB) copied, 2.226857 seconds, 919.7MB/s