For workloads that require super high performance, one can simply use something else... Java, Node.js or whatever. Now that Phusion Passenger supports Node.js as well, it's very easy to write some parts of an app in Rails, and write other (performance-critical parts) of an app on Node.js, and deploy them together on a single server with ease.

Specifically, try using the apr (apache portable runtime), or leverage tomcat (which can use apr) + jruby + jndi jdbc connection pools.

Let rails be rails, your best bet for performance is either making the underlying ruby runtime better or leveraging things that are designed to be high performance.