Didn't know about that adapter. Nice to see there are some options here. The direct Thunderbolt adapter is ideal, but you're right in that it's pretty expensive. Though it looks like it has 2 ports which is impressive.

I still have yet to add a 10G ethernet switch to my network, but Netgear has some that cost about $150/port. The PCIe cards are definitely coming down in price, and would work great in my Linux file server.

For now I have link aggregation set up with 2 ports each on the file server and my Mac Pro, so theoretically I can get 2Gbps of bandwidth between them. That's far from the real case though. The way this particular link aggregation implementation is done, a single TCP connection can only use a single ethernet interface, so you have to have more than one TCP connection to go beyond 1Gbps. That doesn't happen in a file sharing connection unless you are using multiple mount points.