How much more resources (if any) will a full blown Windows 2008 R2 Server running just the Hyper-V role take over Microsoft Hyper-V Server 2008 R2?
I've had conversations with the Windows Team and the difference between the two isn't so much in resources, it's in security and licencing. A full Windows Server 2008 R2 with Hyper-V only and less then a dozen VM's shouldn't need more then .5 GB of RAM for host/parent OS, Up to 1GB if you're running more, and I've never seen a "stock" host OS affect performance in any way... that is until till people do stuff on the parent OS like add backup agents, AV agents, monitoring agents, etc. which will happen the same when you do that in Hyper-V server or server core.
In my conversations with SMB clients and enterprises about the decision of "Hyper-V Server" vs. "Windows Server" the questions we use to help make the decision are never really about performance in this world of 16 core's and 128GB of RAM.:
I know this doesn't specifically answer your question, but if the answer was "hyper-v 300MB" and "Windows Server 500MB" then I didn't want you to take that as a decision to pick one over the other.