You should examine why you might be having a slow insert.

- Is the log growing now? If so, since you have to zero out the file before data can be written., that might be the issue. In that case, you should pre-size the log file (and data file). Shrinking log or data files between refreshes might appear to be giving you space, but if you use it on the next refresh, you haven't really recovered the space and you're forcing more work. I don't think it's Data Compare, but I can't be sure. You might open a ticket with Red Gate and see if there is an issue.

- SSIS can run 1TB in 30 minutes, but it still depends on the log files and storage subsystem to receive that much data. (http://msdn.microsoft.com/en-us/library/dd537533%28v=sql.100%29.aspx)

- The bulk insert task can load data quickly. Again, depending on how you have things configured. The recovery model can affect this, as well as the storage subsystem.

- Do you have lots of indexes on the table? In ETL situations, it can make a difference at times. You might be faster by dropping all indexes and recreating them. Again, you'd have to test this, but it can help.

There's probably other tricks you can try. I'm not an ETL expert, especially at high loads and edge cases, but these are things I've seen/done that have helped in the past.

Disclosure: I work for Red Gate