This implies that you might do just as well leaving macOS running normally on the AS Mac and use normal SMB file sharing over Thunderbolt for this kind of file transfer. If the AS Mac isn’t doing much else at the time, I would expect performance to be similar.
Also, given that the AS Mac is running an SMB server, I wonder how the performance would compare against doing this via a direct Ethernet connection (via GigE or 10GigE). I would expect GigE to be significantly slower, but 10G might be similar, depending on how well macOS is able to saturate that 40G Thunderbolt link during file transfer.