I have a new PC!
List of things in it is here:
https://uk.pcpartpicker.com/list/NgVrRk
It went together quite easily - main problem I had was that I put the CPU cooler on the motherboard before mounting the mobo in the case, which meant it was a tight squeeze to plug in the power cable for the cpu.
Other than that, and some fun trying to set up a new install of Windows to my liking, it all seems to be good. It laughs at Just Cause 3, which my previous rig was weeping about, so I've mostly been explodeding things today.