One thing to think about is as the cpu/waterblock/NB/memory, all watercooled or some watercooled.
Will raise the avg/overall temps on the mobo as a whole, and heat will spread over a givin area.
Even more so with the sys under load.
And give a good 1/4 or more of a degree variance in testing.

Ambient heat so too speak.
Does that make any sense?

IMO something like a thermal camera with time recorded video of said sys
from idle to full load would best show when/where and how the heat spreads.
Plus case airflow and fan orientation would also be a big factor for that type of test.

But then again that is a whole nother hair pulling, long, time consuming, lots of drinking and expensive test in it-self.