If you get stuck I'd first try using the ovftool

OVF Tool Documentation

as exporting large ovfs through the interface tend to time out. I just did a 4TB one and it failed for two weeks. As another alternative is to use vpshere replication, if you set that up, you can let the virtual machine replication while its on. Then when its down shut it down and recover the VM to the other side, the original one will still be there as well.

VMware vSphere Replication Documentation