I don't think comparing RedShift to Postgres is accurate, RedShift was not designed for transactions, it was designed to store/query billions of rows using a columnar storage format...it's more like an analytic database (Greenplum, Teradata). Also, these databases are designed to scale out, and so you usually don't really see compelling performance gains until you start adding a few nodes to help influence parallelization.

With that being said, I'd be interested to see how RedShift compares to Impala.