@florent Thanks for your reply! We have started to migrate thousands of VMs, so disk transfer speed is important for us.. We will also do our detailed tests soon with different threads setting and publish it here. I think threads=1 is a good and logical default, but not efficient. Others might complain if you set it to a higher value. Configuration option would be a real good solution.

Since you're changing all of the underlying hardware that the guest has, Microsoft is going to force you to reactive. You could look at setting up a licensing server to manage these systems and then feed them that information so they can validate and then license. This isn't an issue presented by XCP-ng (or literally any other hypervisor), its a Microsoft restriction to ensure you aren't stealing their software.