Vista - Disk performance comparing different options?

Anyone done any benchmarks (or know and why) when running VPC with
different options for VHD files?

- Fixed disk size (fastest I guess)
- Dynamically expanding disks
- Differencing disks
- Using undo disks

Other things interesting would be performance using differencing disks
when parent file and differencing disk files are on different physical
disks. Or having undo disk and vhd on different physical drives.But I
guess this is hard to test because the data you get from disk might be
in one file only.

Also will there be any noticable performance loss if the VHD file is
compressed (the .vhd file on the host pc).