lawrywild Thanks for the tip on Everest ultimate

Although the trial version doesn't give you all the necessary readings,
I was able to figure out that the GPU was the one hitting the high 70's and thankfully not the motherboard!

Speedfan shows all the readings but doesn't associate them with the proper sensors.

Finally I can relax with accurate idea of what is really going on.

MB 43C
CPU 28C
cores 1-4 42C-47C
GPU 78C (passive cooling)

That's with the case open, now to test with fans low and under working conditions.

much appreciated