I have now done the test on a pull basis
Copied another 7.6GB, this time it took 14 minutes, about 9mb/s
So NFS method is certainly faster, probably by a factor of 2.5 whichever NAS I use.
Pushing the files from the DUO is also around 2.5x faster than pulling them from the NV+
Is this normal ??
I can't immediately see why that would be the case