I want to just export my projects from my old 4.2 system into my new 5.x system, rather than going through the upgrade process, can this be done?
Exporting your projects from your 4.2.5 server and importing to a 5.x server should work, however, expect that the imports will be slow, as the schema conversion to the 5.x format will happen when you import to the new database.
Also, please keep in mind the following:
1) a full export of your entire system (instead of on a project/procedure level) will ensure that you get all of the data - this is the safest way to go, but you should ensure that no jobs are running when you run this command (be sure to turn off the ElectricSentry job too). This will export your full system, including system level information, such as ACLs and properties.
2) If you decide to export on a project/procedure level, you need to ensure that the 4.2.5 projects/procedures are in a 'final' state when you start the export, in other words you should not be making changes (edits) to these while the exports are occurring.
NOTE: If you are exporting WITH jobs, this is especially true, there should be no new jobs being created while you are exporting with jobs.
3) Your access control definitions are not exported with projects/procedures UNLESS you specify the "withAcls true" option - same for notifications, use the "withNotifications true" option
4) The benefit of using the background upgrade script is that it can be run while your 4.2 system is active, so that the 4.2 and 5.x systems can be kept in sync while moving from 4.x to 5.x. If this is not a concern for you, then the background upgrade script can be run while the 4.x system is not active (with the Server service shut down). With the exports, the schema changes will be done on import as previously mentioned.
As with all upgrades, please be sure to backup everything before starting. And also be aware of the change from integer jobIds to full UUIDs (this is documented in the Install Guide), as this was a major change from 4.x to 5.x.