Had the same problem. But was crashing regardless the mission I was playing. The problem was with the CPU overclock rather than the graphics. I had it clocked to 3.465GHz or so using 105x33. It seems like Crysis 3 is very sensible to coreclock changes cuz as soon as I dropped the clock to standard 100 it stopped crashing. I am only using the multiplier now to OC when I play Crysis 3. Hope it helps.