Didn't find a setting for low compression. In Full Backup/Properties/Compression encryption is set to "No Encryption" and split by file is set to "None". Why dies it take so long on this computer (win 7 64b) but not on the Vista machine?
The test works the same way in Backup4all. As your situation is not a general one (not every client has such problems) there are some more options in Backup4all to configure trying to speed up the backup.