Hi oliver8888,
Please try RH 6.4 with Mellanox OpenFabrics Enterprise Distribution for Linux (MLNX_OFED) on ConnectX-3 card you have.
As for the issue with the Windows Guest, it seems to be a real issue.
Please contact support@mellanox.com, and open a ticket to get updates on our progress.
I'll update this thread the moment I have more information on the Windows Guest issue when running in Pass Through mode.