VirtualBox massively outperforming KVM - comments?

I wanted to see what would be the best performing (for my needs) virtualisation solution. I kept reading KVM outperforms VirtualBox, so I installed KVM and gave it a try. However, the guest system seems sluggish compared to VirtualBox so... I compared the two.

Host:
Core2Duo 2.5GHz, 8GB RAM, SSD
3.18 kernel, latest VirtualBox

On each VM I:
- installed the same fresh XP 32bit system
- installed appropriate guest additions
- I did NOT enable 2D acceleration on VBox, and I DID select QXL graphics on KVM (so if anything, VBox got a shorter end of the stick here)
- run Passmark benchmark.


Here are my findings:

KVM / VirtualBox

CPU Mark 1147 / 761
2D Graphic Mark 70.3 / 307.9
Memory Mark 434.4 / 371.1
Disk Mark 290.7 / 993

Samba Sequential Read: 6.3 / 84.5
Samba Sequential Write: 11 / 40.1
Samba Random Seek + RW: 2.54 / 44

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Overall passmark rating 298.7 / 463.4
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So it appears that apart from CPU and Memory Mark (in which KVM edges in front of Vbox) VirtualBox simply obliterates KVM. And don't even get me started on Samba share performances, where KVM does just absurdly bad.

I am quite surprised native KVM virtualisation compares that badly to VirtualBox. There either is something very wrong with KVM, or it just can't run Windows guests properly.

Any comments welcome.