Made me think of this:

I got a 10G ethernet network card for my NAS only to realize it has to overlap with my modem's supported bandwidths (IIRC 2.5G, 5G).

Knowing nothing about the space, I had assumed it would use max(node1, node2), but instead it negotiated a 1G link. So it was faster to use the mobo's built-in 2.5G port.