No PC related build is complete without careful cable routing. I 3D printed some simple cable management loops which clip into a base plate attached to the side with some transparent double sided tape

After some careful research it turns out if you're using CAT-5E cable and gigabit then there is no 1 meter minimum length as there was with 100Base ethernet to prevent reflections. So I pulled out some CAT-5E and started crimping. I had a bunch of male molex power connectors (or are they female? molex is kinda both at the same time) so I crimped on some wires and then it was just a matter of connecting up the ATX controller and we're in business!