Re: GPU at $BUSID$ has fallen of the bus
You might want to try to disable wmi completely. Currently I'm also in the process of finding out how to do that. In my case, the Clevo570RU Notebook, all this mess is not resolved even when completely deactivating ACPI, so its not even related to that (although this machine has a hell lot of ACPI related issues I need to get fixed).
The only useful workaround I came up with up to now was to revert xorg to version 1.10 and use a 260.x driver which is a major pain the more recent your distro is. Funny enough its even possible to use OpenCL with such old drivers if the OpenCL libraries of the newer drivers are still around.