Distance to TjMAX for Nvidia GPU

NVIDIA GPUs (unlike Intel CPUs) report absolute temperature, not an offset from the maximum temperature.
They also don't report their maximum temperature, so it's not possible to reliably determine this value. Basing the maximum temperature on published maximum ratings is not reliable, as this might change from part to part.
I have at 100% continuous load CPU, 100% continuous load GPU, GPU fan 64% RPM - GPU temperature is 75 - 77C.
This is the norm or do I need to worry?