I don't know how big your squidguard blacklists are (its a good idea to include details when asking questions), but the largest one I could find was 20MB [...]
My biggest list is 22MB and gets daily updates. But because it uses much RAM when be loaded I check all entrys one time per week so that only online servers are in these list. So the total size is now about 16MB. All in all that are 16 Lists between 1 and 16 MB. No problem for your internet connection - the connection of my client sometimes gets only 42kb/s!
Anyway, rsync sounds like the most appropriate mechanism to transfer these particular databases.
My blacklists should be available for everyone not only for those who can connect with my server via ssh...