What is the best approach to create a reference version of schedule and baseline in P6?

We have an initiative to produce metrics on a large number of projects from P6.  All of the projects/schedulers are not on the exact same update cycle, so we are trying to determine the best way to have a copy of the project & baseline that will not be modified.  The individual producing the metrics requested a seperate instance of P6 be created and import XERs from the schedulers on a monthly basis.  Another option is to create monthly archive copies of the project in a node specific to Metrics, limiting users to read only access.  Are there any more