Part of your problem may be the distance between data centers / server locations. Especially if they're in different domains.

Sometimes doing batches can help speed things up, but I don't know anything about DB2, so I'm not certain this would work for you. You might consider getting a network admin to sniff the network while you're doing this transfer to help identify hardware / network issues that may be causing the issue.

Also, how fast does the SELECT from SQL Server work? Check this out in SSMS. If it's quite speedy, then your problem isn't SQL Server. But if it's quite slow, then you have code tuning you'll need to do before pushing the data to DB2.