For kicking off a new week of Linux benchmarks, here are some results of a high-end Intel Extreme Edition workstation when comparing the bare metal host and KVM virtualization performance between Ubuntu 12.10 and the earlier Ubuntu 12.04.1 LTS release and then the RHEL-based CentOS 6.3.
This benchmarking was all done from an Intel Core i7 3960X "Sandy Bridge" Extreme Edition system with 8GB of RAM and an OCZ Vertex SSD. Each operating system was benchmarked with its stock configuration and packages. When running the KVM-based virtual guest machine, each time the same machine settings were specified through virt-manager and the guest operating system matched the host.
The "bare metal host" results is the raw-metal performance without any form of virtualization being used. An attempt at a three-way virtualization comparison with Xen was also attempted, but Xen had issues on this hardware/software configuration with Ubuntu 12.10 at the time of testing. All benchmarking of the host and virtualized guests was done through the Phoronix Test Suite software.
For additional reference, from earlier this year with the Long-Term Support (LTS) release of Ubuntu 12.04 was also a virtualization comparison of Ubuntu going back to 8.04.4 LTS.