I have that card and use 258.96 drivers and the game runs fine. FFXIV makes my video card run hotter than any other game. Run a program to monitor your GPU temperatures and see if you are getting over 90 degrees celcius while in the game. If you are overheating download MSI afterburner and see if you can adjust the fan speed using the utility. It should look like a chart and you can set at each temperature point, how fast the fan should be utilized.
Monitor your CPU temperatures and make sure that it is not overheating.
Oh and did you update your motherboard chipset drivers?
Oh! And it may seem a simple thing, but check your airflow, especially if you're running things a little extra hot (overclocking and all that), doesn't matter how fast the fans are going if the hot air ain't going anywhere. Check for dust too.
I know those are really basic solutions and they're probably solutions you have already looked into, but they're solutions people tend to overlook when things go haywire.
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