17.12 is ANCIENT the problem with that driver is you lose a ton of game optimizations. With HBCC not on, undervolted, and that old driver it explains the low power consumption. At least try last stable which is 19.1.1
I haven't seen any of the issues you mentioned although I haven't played Witcher. The only game where I had notably poor performance was Quantum Break and strangely that game once I got past a certain point just plain ran better. I think it was just poor programming. Also my monitor is 100hz Freesync, I run at 3440x1440, some games with Freesync off have a lot of microstutter (like For Honor) but with Freesync ON run smooth as butter. But then Hitman actually runs better without Freesync, go figure?
i took you're advice and updated the driver to 19.1.1, im not sure if its installed correctly though as when i click the search for updates button in radeon settings its still recommending i update to 19.1.1. i think this problem is being caused by windows as my machine wont restart. I can shut down or start from an off state but not restart, it just shuts windows off and then i get a blank screen. pc is on but doesnt go through the post startup. this is on windows 10 pro. I had this issue previously on ltsb but cant remember how i fixed it. after a quick read this seems to be a common problem with consumer W10.
anyhoo, with the new driver, exclusive fullscreen doesnt work properly. got a weird widescreen border. borderless fullscreen is fine though.
things i've tried.
restoring all bios/windows settings to default.
clean install of windows.
booting with 1 drive and 1 ram stick.
removing all peripherals/usb sticks
disabling fast boot/sleep/hibernate through settings and with commmand prompt.
disabling uac
fixing boot sectors through cmd
disabling superfetch through services.msc
tried restarting with my 980ti in and it wont restart.
used a different psu
replaced mobo battery
nothing fixes the boot issue. next ill try running a live linux disc and checking all the hardware and partitions. At this point im at a complete loss. i sincerely doubt its hardware related, it must be a bug within windows itself.