For anyone reading this, I think I figured it out!

I'm using a USB adapter, and it was originally plugged into my rear USB ports. For some reason, power to those ports is reduced when the video card is under strain (despite having a sufficient PSU). (This is detectable by running a set of ~300 pings to your router while you mess with the video settings).

I solved this by plugging my adapter into my FRONT usb ports, which for some reason don't face this power issue!