So the powered usb card didn't help.
Think I'm going to install a fresh Windows into a spare hard disk and see if it plays ball then. To be fair my current install is a couple of years old so a new clean install might be sensible.
Going to speak to hp support on Monday and get a new cable, hopefully on warranty
I have a Reverb G1 and built a VR driving sim for someone else using a G2. My experience with the G2 prompted me to buy another G1 as a backup. The G2 was just too much hassle.
If you don't need the adjustable IPD, I recommend getting a G1 (probably mostly refurbs and used out there now). The two different X570 builds both worked well with the G1.