If you have been looking for VHD performance data the paper below should give you a lot of what you have been looking to find.  The paper compares VHD performance on Windows Server 2008 and Windows Server 2008 R2.  It uses the new Native VHD implementation for R2 and loopback VHD 2008.  There are some Virtual Machine (VM) comparisons as well for completeness.

http://download.microsoft.com/download/0/7/7/0778C0BB-5281-4390-92CD-EC138A18F2F9/WS08_R2_VHD_Performance_WhitePaper.docx

  Enjoy,

     Tony