That doesn't seem to explain why it would suddenly start doing it 6 months after I last upgraded my PSU.
I didn't make it!
GPU's do die, ya know, though I don't know if they gradually degrade in power quality.
Yeah, it's a driver thing. When my GPU was overheating I couldn't start my computer. >.>
Are you sure your PSU has adequate amperage on the 12v rail for that GPU? Also, do you have the GPU mounted on it's own rail?
Before opening it, I tried to do one last thing; Load the factory defaults in the BIOS. After putting the vital settings back to their "working" state, I tried with the 178 drivers again, and playing for an hour I haven't experienced a crash yet. If it happens again, I'll have to open it and do a proper inspection.
Also, don't forget when you clean your case to blow out trapped dust you can't see. Major culprits can be PSUs and GPU and CPU HSs.