>I am also quite certain that the CDX is written (roughly) in the same way - as it needs to. This is apparent, again, from the defrag reporting, but also logically necessary so that other users can see the records as soon as possible.

"it ain't necessarily so" - When multiple clients request content from the same file on a file server, the OS on the server first checks to see if the content is available from cache. If it is available from cache, then this is where the content is sourced from. This should also hold true for new/updated content about to be committed to disk.