With Mir likely soon entering the Ubuntu 13.10 "Saucy Salamander" repository, a new version of Mir was tagged this morning in the project's Bazaar repository. Mir 0.0.5 incorporates all of the latest work within the Mir repository, particularly over the past several weeks.
Meanwhile, the Kubuntu project announced they will not be switching to Mir/XMir. The KDE-based Ubuntu spin intends to stick with X.Org and then switch over to Wayland when the upstream support is ready. "We'll be staying with X on the images for our 13.10 release now in development and the 14.04LTS release next year. After that we hope to switch to Wayland which is what KDE and every other Linux distro hopes to do."
Lastly, Canonical is in communication with me now about Mir benchmarking. Mir benchmarks will likely be coming on Phoronix soon.