If your dynamic site loads slower then a static site, you are probably doing needless database round-trips, redirects, synchronized writes, or html rendering.
..Which in turn gives you better page rank.
..Which gives you more traffic.
But that's it.
..Well besides that it also gives you lower bounce-rate.
..Which means higher conversion.
..Which means higher ROI.
So there's that.
If it takes like ten seconds to render the site on the client, then 10ms gain on connection time wont help much.
Test tool: http://www.webpagetest.org/video/
When all css, fonts etc are cached on the browser client, then there's almost no gain with CDN.