OMG what a total mess the 12.3 driver is. It crashed and rebooted the PC on first install (first time that's ever happened, and no I didnt do a DDU as never needed to previously). Then with only part of a driver installed it wouldn't load up or uninstall, so I rebooted again. Then it did uninstall and after a reboot I then attempted to re-install but that failed as the previous driver had not properly uninstalled (allegedly). I rebooted again and this time it uninstalled successfully and then finally installed, on 3rd attempt.
Then onto the testing. So 19.12.2 lost me 6 FPS over 19.12.1 in the Borderlands 3 benchmark using my Vega 56 1637 GPU + 980 HBM + 15% PL OC profile. This driver lost me 7 fps!!! Although sceptical the old profile was the issue (XML looks identical), I even tried creating the profile from scratch but same result. So back to 19.12.1 I go, again. This is the sort of bad experience that could drive me to Nvidia next upgrade if it goes on much longer