The 101 mins reported above was a reporting misinterpretation. Actual time was 56 mins, but 4 mins was spent in a shutdown/restart to force the flush at 500GB. So with managed dirty flushing the big mac will be network limited, just as maxi. And that also implies that our mac mini should also be network limited, at about 50 mins. So once the details are worked out, macOS will be a first class citizen. And instead of prompting for OS config, we can poorly-configured (default) Linux on the same path.
(edited)