Sadly it's not a fair fight, of course it'll beat Mongo (even though Postgres is ACID). I would be more interested in comparing the biggest machine you can get

Sadly it's not a fair fight, of course it'll beat Mongo (even though Postgres is ACID). I would be more interested in comparing the biggest machine you can get on AWS running Postgres with a cluster of smaller machines running Cassandra. I expect Cassandra to win, but of course it's not consistent.