CentOS virt - Mar 2016 - Virtualized Server 2008R2 can't boot with multi-core

I previously tested a fresh install of Windows 2008R2 using the free
evaluation download from Microsoft and worked without much hassle.

However, when converting an actual physical W2008R2 machine to virtual
using Windows' bare metal recovery, it would not boot with more than 1
core assigned. I''ve tried various suggestions such as
- adding/removing <hyperv><relaxed
state='on'></hyperv>
- setting cpu type to core2duo and requiring nx

But neither helps, basically a brief blinking cursor in the upper left
corner after BIOS/EFI then blank.

Any suggestion on how to fix this?

Using CentOS 7, yum updated to latest ( 3.10.0-327.10.1.el7.x86_64)
Physical server is UEFI so loader set use ovmf-x64/OVMF_CODE-pure-efi.fd