Yesterday marked the final kernel freeze for Ubuntu 14.04 LTS ahead of the distribution's official debut in two weeks time. Ubuntu 14.04 LTS is using the Linux 3.13 kernel but there's many patches that were back-ported from Linux 3.14 and even yet-to-be-mainlined work. As one example, I already wrote about Ubuntu 14.04 having its own special Intel "Broadwell" driver.
For system administrators or those just wishing to dive into the Ubuntu 14.04 LTS kernel to see how it differs from a vanilla Linux 3.13 configuration, Leann Ogasawara of Canonical has posted a mailing list message with various resources that outline the patches they're carrying with their 3.13-based kernel, their kernel configuration, the configuration against Ubuntu 13.10, etc.
We've already delivered many Ubuntu 14.04 performance tests and benchmarks but more are on the way.