Virtual Disks and performance..

Quick question for you all..

I've set up a virtual terminal server cluster and I'm running all of my

machines off differencing disks from a master "sysprepped" 2k8 vhd.

Would this improve performance, or am I better having a load of individual

..vhds?

My thinking is that any references to the master image should then be cached

and so available to all the VM's. Am I right in thinking this? has anyone

done any benchmarking on this issue?

Cheers