When starting with a few disk-focused tests, there is the initial create operation within CompileBench. KVM virtualization on the Intel Core i7 3960X was running at 89% the speed of bare metal for this disk test while the AMD FX-8150 KVM performance was at 87%. The VirtualBox performance for this single Dbench client run was well behind the Kernel-based Virtual Machine. Xen on the Sandy-E setup came in close to KVM.
When doing eight threads of 64MB random writes with the Threaded I/O Tester, KVM performed quite poorly. Oracle's VirtualBox was multiple times faster on both the Intel and AMD systems while Xen on the i7-3960X faired the best of the virtualization methods.
Switching over to the computationally-intensive tests, beginning with Google's libvpx VP8 encoding test, KVM on the Intel Sandy Bridge Extreme did better than the AMD FX-8150 Bulldozer (84% the speed of bare metal vs. 75%). However, VirtualBox on the Intel system did much worse than the same VirtualBox installation on AMD's latest-generation platform. Xen did remarkably well at 98% the speed of bare metal for the Intel system with 12 logical cores.
With the x264 video encoding test, KVM on Ubuntu 12.04 LTS was running at 82% the speed of bare metal for Sandy-E and was at 86% on the Bulldozer setup. Xen continued to perform quite well on Intel while the Sandy Bridge Extreme performance with VirtualBox continued to do quite bad relative to how VirtualBox 4.1 was running on the AMD hardware.