Mainstream copper connections can't really go above 10Gbps. Also 10GBASE-T runs hot. If you think you will ever need more speed then just running some fibre makes sense - just a transceiver upgrade required in the future for higher speeds.
I remember when it was "mainstream copper connections can't really go above 100Mbps" and we ran fiber. Not that there isn't some physical limit to how much data you can reliably push down 4 pairs of copper (that sort of physics isn't my bag), I just wouldn't bet against running 100G over Cat13++ or whatever standard emerges down the road.
But, yeah, fiber is always gonna be more 'future proof' and damn my 10G gbics do get annoyingly hot.
You can get a good idea of the current state of the art in pushing bits over copper in internal PCIe cables. Those are short, thick, and pricy and the connections even within a single chassis often needs a retimer / redriver chip [0] to recover signal integrity.
That's some pretty cool tech, but 'State of the art' wasn't really what I was talking about. I mean at some point, there's likely a physical limit to how many bits per second that can be pushed down an 4-pair copper networking cable of current girth no matter how clever we get. My bet is that it's north of 100G; a beer to the winner.
