A note about Compojure: they're using Korma for database access. Korma is an abstraction layer that's more Clojure-friendly than using SQL directly, but lighter than an ORM. Using clojure.java.jdbc might produce higher performance.
It's just important for people to be aware that "Compojure" actually represents "one possible production-ready stack that uses Compojure as the routing component", as do several other items on the list. I don't mean that as a criticism - just clarification.
But yes, the performance of a reasonable web app stack on Clojure is very good.