Ubuntu 11.10: Xen vs. KVM vs. VirtualBox
KVM also was the fastest for the MAFFT molecular biology test.
KVM was also the most efficient in handling OpenMP.
When switching from stressing the CPU to the disk, KVM was still leading while Xen quickly jumped up to compete with KVM and VirtualBox quickly receded. All three were tested with their default disk formats. This was for the Apache web-server workload.