[CentOS] unison versus rsync

Anyone got any actual comparisons between unison and rsync specifically related
to the performance of synchronization of large data sets over slow links?

I have a huge tree to start replication of Friday and know that if I sync the root
paths it will take ages and with the lack of any overall state of progress this won't
be optimal as its likely to fail for whatever reason before it can finish. Initially
I just thought I would break it down to several smaller jobs but that becomes a burden
to maintain...

We use bacula internally  but sending the diffs would be cumbersome as the individual
files would be rather large...

Thanks!
jlc