KVM's lead over VirtualBox expanded when looking at the x264 H.264 video encoding performance where KVM was able to run at 87% the performance of the host and VirtualBox 3.2.12 was left at 74%. The VirtualBox 4.0 Beta 2 performance had again regressed compared to the stable 3.2 series.
MP3 encoding was not particularly interesting.
The same goes for FFmpeg.
Where VirtualBox was able to reliably pull ahead of KVM was with regard to the loopback TCP network performance when timing how long it took to transfer 10GB on the loopback interface. KVM took twice as long as the system host while the VirtualBox overhead was much less, although it was again slower with the newest beta release.