FC-6 VM On F11 Platform

I recently upgraded one of my virtualization platforms from F10 to F11. It is significantly more stable and refined. An odd thing happened, however. The target system is an AMD-64x2 with 5G. Its was hosting:

FC6 application server
F8 VNC server
WXP Pro with RDC (need it for my current contract)
F10 on 4 node cluster for clustering R&D
F8 on 2 node cluster for web development
F8 application server

Under F10, the box gave great VM performance while at an idle.

Under F11, the FC6 VM pegged the virt-manager's performance graph at 45% of the physical CPU cycles. Yet, within the VM, top saw nothing. Effectively an entire core spinning away on nothing! I re-imaged (via kickstart) the VM as FC8, and now that same machine sits at half a percentage point. I'm not sure I have an explanation other than a different kernel or virt drivers.