We need to run the lighthouse tests against the same pages on each test instance to get results we can compare.

We can set up a data sync, though this shouldn't remove any of the other content, since it might be used while testing. We could use a meta field to mark these posts, and maybe write protect them so they're not accidentally deleted/changed during testing. Another option is to just run the sync before each test. That sync shouldn't insert new posts, but update the specific post's content/status/relevant meta fields.

Ideally those pages don't have blocks that would pull in content that could be different on each test instance, to keep each test run as identical as possible. Maybe that can be achieved by using a specific tag in these blocks (e.g. Articles), then only tag test content with it?

We can manage this test content in the defaultcontent instance.

It can be the same content that is used for the visual regression and a11y tests. These currently are not guaranteed to be the same across instances so would benefit from that too.