Remember the line in a "Princess Bride" when Indigo Montoya says "You keep saying that word, I don't think it means what you think it means." This is one of those things. For example when my MoBo utility display "MoBo Temp", that is actually a weighted average of several sensors.... soi I don't know what or when i should be concerned about. The problem with these non standard sensors, is we don't always understand what it's measuring. MSI has a feature in their GFX cards for example...
"Another feature is called Hybrid Frozr, and this refers to the ability to control both fans independently. Enabling this functionality is a six-pin fan header on the PCB. In automatic mode, one fan is controlled by the GPU temperature while the other is controlled by temperature measurement ICs dotted around the PCB. "
I have asked about that before on my 5 year old build ... the 780s say 21 and 22C ... is that the hottest point ? is that an average ? i can't judge anything cause i don't know what it is measuring. I asked Asus TS, they didn't know.