One thing to note, is that just putting some/all of your content on a separate sub domain will allow you to get some of the benefits of the cdn, 2 browser threads per subdomain. However, when you get up to 4 total domains needing dns, including analytics and other providers, the dns lookup takes longer than waiting on another thread in the browser to download that image. Also to note, when js files or css files load and import other files, they halt the browser from allocating any new threads on any subdomain until they are done processing. So just putting your js files, lower in your html generates a healthy speed increase if you have a lot of it.

javascript_include_tag & stylesheet_link_tag also accept a :cache => true option, which will merge all your stylesheets/javascript. Won’t minify them though.

You also might want to take a look at New Relic’s RPM suite for performance monitoring.