Update
Update
Couldn't resist trying the 14.4WHQL's again, this time from a solid 13.12 installation.
1)
Created a restore point with the 13.12's installed, crossed my fingers, then used the same
amdcleanuputility.exe program (that hosed my original 14.4WHQL uninstall) to uninstall the 13.12WHQL's.
Worked perfectly. Upon reboot after uninstall, system was normal (hallelujah!)--no dead/inaccessible USB.
2) Next, during the initial attempt to install the 14.4WHQL's the installer functioned to the point of the first blank screen indicating initialization of the 3d driver (which is supposed to initialize in that manner twice on install, and twice during uninstall)--but then the screen stayed black and did not recover. I waited until all drive activity had ceased and then did a hard reset of the system.
3)System came back up normally, but with a partial install of the 14.4WHQLs. I again began a second, normal install procedure of the 14.4WHQLs from the CIM, on top of the first unsuccessful attempt, and the second attempt initialized all 3d drivers normally and finished without errors, and upon reboot 14.4WHQL had been successfully installed.
Yesterday, I had time for a gaming session lasting a few hours and I noticed no anomalies, errors, or Alfred-Hitchcock-profile blue screens (what blue-screens in Win8 remind me of.)
I am not ready to try to uninstall the 14.4WHQLs at the moment...
In fact, I will not uninstall them and revert back to my 13.12WHQL restore point unless I get another SYSTEM_THREAD_EXCEPTION_NOT_HANDLED(atikmdag.sys) error, or something similar.
These drivers are still shaky, imo--as I shouldn't have had to install the 14.4WHQLs *twice* to get a proper install (perhaps the amdcleanuputility.exe is a bit too aggressive?) So we shall see. I'll update this post with further info should it arise.