Virtual Hard Disk Performance Whitepaper
Until now not much has been documented about the performance of VHDs by Microsoft. However Microsoft has published a whitepaper below that should give you a lot of what you have been looking for when it comes to VHD performance.
The paper compares VHD performance on Windows Server 2008 and Windows Server 2008 R2. It uses the new native VHD implementation in Windows 2008 R2 and loopback VHD. You can download the whitepaper at http://download.microsoft.com/download/0/7/7/0778C0BB-5281-4390-92CD-EC138A18F2F9/WS08_R2_VHD_Performance_WhitePaper.docx
Patrick Lownds