I have a similar issue, except its an opposite...
Current temps idle:
System 35C
CPU 36C
AUX 52C
HD0 31C
HD1 23C
HD2 27C
When I run SuperPi 1M
System at load temps:
System 35C
CPU 44C
AUX 22C
HD0 31C
HD1 23C
HD2 27C
I can't understand why the temperature reduces under load, I've searched...