[Logician]

instead of using the entire "user" table, I suggest writing a script to read relevant data from one of them and insert it to the other..

If you upload the entire user table, there will be some clashes in the new board, such as post numbers. But if your new board has no users yet, uses the exact styles with the first one, have same user groups, coppa settings, user titles, you can apply Xenon's suggection and then run some SQL commands to reset post numbers, join date, last visit, last activity, last post fields..