Okay, so I thought I'd update....
I figured out what the "problem" was. When I'd reinstalled Windows I'd been using the latest chipset drivers directly from AMD (CPU), Nvidia (GPU) and Asus (Motherboard). Likewise, I'd grabbed the latest gigabit network drivers from Intel and the 2.5G drivers from (I forget, don't hate me)... anyway, despite these being all the current drivers directly from the respective OEM sites I never got past the spinning logo animation of doom.
At wits end and by sheer chance I had accidentally deleted my drivers folder on my Windows 10 USB drive, so when it came to reformat for the 19120398217th time, I decided to grab all the drivers directly from the Asus website (except for the GPU, I'm not a monster). Boom. Installed no issues
It does mean that the first time I ran Windows Update it wanted to update the chipset, network and USB drivers etc but even then all was good. I swear it makes no sense because I had used all the same versions installed manually without success so the fact that Windows installed old drivers by default then updated me to the latest drivers BEFORE I had installed G Hub AND it worked, still baffles me.
Morale of the story? Use outdated drivers kids. Or at least try some.