I second the virt-io question.
Beyond that, it would have been interesting to compare networking performance.
As general, these results more-or-less mirror the VBox vs. qemu-kvm benchmark I did in-house when we selected our VM solution (qemu-kvm).
DEV: Intel S2600C0, 2xE52658V2, 32GB, 4x2TB, GTX680, F20/x86_64, Dell U2711.
SRV: Intel S5520SC, 2xX5680, 36GB, 4x2TB, GTX550, F20/x86_64, Dell U2412..
BACK: Tyan Tempest i5400XT, 2xE5335, 8GB, 3x1.5TB, 9800GTX, F20/x86-64.
LAP: ASUS N56VJ, i7-3630QM, 16GB, 1TB, 635M, F20/x86_64.