As a follow up, I noticed threads from earlier this year on here, guru3d and reddit talking about freezing and BSODs with freesync turned on, so I followed the advice from that, turned off freesync in the drivers, vrr in windows and freesync on the display, and the freezing went away.
Only now I have two issues, instead of freezing I get screen flicker above 60Hz under the same cicumstances, enabling then disabling HDR, etc, and as I suffered from the high idle power draw issue, which was fixed for me in recent drivers, but only when I have freesync enabled. So I ultimately have to choose between my system locking up, or high idle power draw and screen flickering which requires a reboot every time.
I've only had the card for under two months and am already at my wits end on this. I tried to get a refund, but was told by the retailer that I can't as this is a driver issue and not a hardware fault.