Is there an up to date benchmark / API comparison of document databases somewhere that includes it?

If you need JOIN in document db, you are doing it wrong.

Says who? Why does DBRef exist? I would like to see any non trivial application that doesn't use id's to reference between documents. Almost everyone is doing joins, just in the application layer, which is the worst place to do them.

http://docs.mongodb.org/manual/reference/database-references...