I would love to see postgres in the mix.
For this little test (on my macbook), Mongo was the fastest. PG took 1 1/2 times as long, and Orient took 4 times as long as Mongo. All 3 were driven by a Java client connected via a socket to the DB on localhost. (Orient could have been "in process", but I wanted it external as if on a server)
Of course, the main use-case for Orient is reading back graph chains, so it's a horrible test. However, what we need is a supplemental store to dump some flat junk as the app runs.