Switch your blind faith to Go (s5cmd) and get ~1200 MB/s upload speed!
zfs send tank/pgdata@snapshot | pbzip2 > mybackup.zfs.bz2
s5cmd cp mybackup.zfs.bz2 s3://mygooglebucket/
https://github.com/peak/s5cmd/blob/master/README.md#Benchmar...
zfs send tank/pgdata@snapshot | pbzip2 > mybackup.zfs.bz2
s5cmd cp mybackup.zfs.bz2 s3://mygooglebucket/
https://github.com/peak/s5cmd/blob/master/README.md#Benchmar...
Overall, I didn't see if they've identified the bottleneck. My guess pbzip2 is the slowest, ssh second. For compression bw I'd check zstd. For ssh there are various cipher/compression options. Or perhaps skip altogether and use wireguard.