The KVM-virtualized tests of the multi-threaded GraphicsMagick tests were quite interesting and did extremely well against the bare metal numbers. Strangely, for AMD's Bulldozer in these OpenMP tests some of the KVM results were faster than bare metal -- including when factoring in the standard deviation between the multiple runs. AMD's new architecture with KVM virtualization seemed to act strange in this OpenMP test and a few others. VirtualBox for GraphicsMagick was noticeably slower than KVM.
In the popular 7-Zip compression test, the relative KVM performance between the Sandy Bridge and Bulldozer processors was the same. However, VirtualBox on Sandy-E continued to be very sluggish while Xen still did quite good.