I was working on a project in 2010, when I had to move the newspaper website from Typo 3 to Drupal 7, and the fastest way at that time was to export all the content as xml and then parse them on drupal (Xpath), We tried to do this at one time, but we had problems on 4Gigs. So, we split xmls per year, and each file had less time to parse and the file size in MB, and everything went fine. Other readings suggest that the maximum file may depend on your bar.
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