The driver is not the problem, it's the gpu. When it says display driver stopped working it means the gpu crashed for whatever reason. What you were experiencing was thermal crashes due to an unstable o/c - the only way the gpu could tell you "I can't do this" is to crash and say the driver died.
You have already answered your own question regarding can you push it farther - you lowered the speed (and thermals) until it was stable. You can try MSI afterburner for custom fan curves, or go to water on the card, but generally speaking, you have reached the max o/c for the card.
Thanks for the reply mark