Synology actually supports the old (non-encrypted) rsync protocol, too. On a trusted LAN, it runs much quicker that way than with rsync-over-ssh...

I just finished slurping all of my files off an old Synology and onto a TrueNAS server. Unlike the article here, my Syno is 2x1Gb in a LAG, so I was really only getting ~1Gbps at max.

One disappointment with TrueNAS is that it doesn't support SMB-MC unless you put each interface on a separate subnet (which is a strange limitation because Samba itself doesn't seem to suffer from this, since synology handles it fine)