I spent the last week testing ext4/btrfs/zfs on Linux and I found that zfs is rather slow and btrfs has improved its performance a lot in the last years (I should refined the script a bit, upload some graphics and make a post).

https://gist.github.com/liloman/d525131fab9b9a440140905921e9...

I'll give it a try on bcachefs. :)

The script needs a 512MB spare disk partition and some basic changes but the fundamental work is there.