The difference between 30c at idle and 70c when pushed is not that far as the GFX temp increases massively when rendering 3D graphics, run a probe on it and see how much and as such overall system tempratures should not be discounted... the motherboard probes also do NOT measure the temperature of the processor they measure the temperature of the air under the processor as the probes are located in the CPU socket.. If this is registering 30c it would be fair to suggest that your actual processor temps are a little higher than indicated.. These are not accurate

a GFX card never requires voltage hikes for stability as these have greater bandwidth available than the motherboard.... what's the voltage going to your processor......If its not heat.... I bet you have a low 5v line even when on idle