Hi follow up on this one - we have tested and Active Auditing is not the root cause; the issue remains with it all disabled. The root cause appears (currently) to be purely the amount of data (ABAP names, variant names, calendar names, etc.) associated with the SAP system.
This data doesn't scale well as it all gets encapsulated within the SAP System object; so even if you're just trying to edit that it loads ALL of this data into memory (or tries to).
We are continuing to test and investigate - an obvious solution is to proactively manage the amount of data you import for a SAP System; however where do you set limits? A system improvement could perhaps also help here.
If I remember I will post an update here when resolve and maybe blog on this.