First.
It's more efficient to use a small hardware router for NAT. They make forwarding decisions at the hardware level, so therefore they can make them with less latency, and consume less power.

Second.
You aren't actually creating a machine with 7 ethernet ports. There is still only the throughput of one. Also, if you are doing major file sharing, you will run into collision hell if you're using a hub.

In sum:
Don't use software NAT unless you really have to.
If you have a lot of traffic from multiple nodes, don't use a hub unless you really have to.