Like others have mentioned, Postgres and Redshift are very different animals, Postgres is a row store and Redshift is a column store. On large data sets analytic queries that return a few columns will significantly outperform a row store DB.
We have found that Redshift is comparable to other columnar databases we work with, while we cannot publish any comparative benchmarks, we did put a blog post on what we found (link in another comment here)
We have found that Redshift is comparable to other columnar databases we work with, while we cannot publish any comparative benchmarks, we did put a blog post on what we found (link in another comment here)