timmmay:
Knowing nothing about macs, I guess you plug them into the same Ethernet switch. You'd want it to be gigabit at least, even that is only 125MB/sec.
Probably closer to 100MB/sec after allowing for protocol overhead.
Leave it running a day and you could transfer 8TB. If the main OS is on a 512gb ssd you could transfer it all in an hour or so.
The OP doesn't really say how much data needs to be transferred. Usually if one has many TB's of data, you would keep the OS and data on different drives.