>If all you are doing is reading single rows from a single table using an index, then yes Postgres is overkill and other solutions may perform better

No, not really. Mysql will perform very slightly better if you are doing just simple selects and they are all with a single connection. But it is a pretty small difference, and it goes away if you have anything else happening at all. This notion that postgresql is somehow "overkill" because it isn't broken is silly.