My less than stellar DSL internet has no trouble with FTM sync. However, I only sync manually and up to ancestry. Hints and records found are downloaded manually and added to FTM database on my mac. Only then do I start a sync. This avoids duplication like census…residence facts. After a sync I also check each of the people involved to see if anything funny has happened.
If RM8 becomes stable on the mac I plan to switch to it for larger text size and better cleanup tools but at present it remains unusable for mac users.