Looks like I have a defective CPU after all this. The machine always had the odd stability issue that we never tracked down but enabling these options seems to have made it hang every time. I ran with one CPU in a socket at a time and I have one good CPU and one bad. It hangs every time while the other boots with no issues and I can see passthrough enabled in the node details.
On a related note, how do I remove an old host from the Engine Compute->Hosts view? There doesn't seem to be an option to delete/forget it? It seems to have a Status of Unassigned with only Restart/Stop options in the Managment drop down menu. I want to reassign the node name to the reinstalled host.
Shareef.