You have made some good decisions in choosing your components. Understanding your motherboard may be the most important factor in solving many problems. Recommend you read TFM.
Always think about H E A T when performance all of a sudden becomes erratic.
Go into the BIOS and MANUALLY set the equivalent "fan expert" or similar utility for your mobo mfg. When temps rise on cpu the fan(s) will increase speed. Personally believe in a radiator and push/pull cooling...very quiet and super effective!
Be sure in BIOS that your memory is at RAM stated speed; 1333, 1866Hz, etc. Adjusting memory voltages and timings is NOT recommended unless you are experienced with these components.
Different drivers can effect temps. Go for stability FIRST. Find a driver where NO problems are encountered, then begin the laborius process of adjusting until something happens...
Pair of 7970s can put out serious heat. I have a build with a pair of them and I ALWAYS keep the fan speeds at 45% or less unless overclocking! Velcro an outside 120 mm PWM fan in the gpu exhaust area to assist the huge amounts of heat to be drawn OUT OF THE CASE. Case airflow (positive/negative design) should be updated, upgraded and ALL components (including all fan blades) should be pristine clean in the case.