Managed to get the AMD S7150x2 working with xcp-ng 7.6 week ago. No idea how it stacks up performancewise with anything else as it is my first adventure in VM shared video.
I can post details Monday when I am back I the office, but I just installed XCP-NG and loaded the Citrix driver from AMD's website and it worked. Much more sane install than my attempt at Hyper-v. The mxgpu settings page gives me the ability to set the you slices and everything. Performance in one test guest feels pretty decent.
Overall I'm very impressed by XCP-NG so far.