
The "DeltaT(chillin - Chillout) v Flow-rate" plot suggests more heat is entering the system in the range of flow rates showing enigmatic cpu Temp rises.
Translated to Watts:-

This heat will enter through both "cpu/mb" and "the rest of coolant loop"
In steady-state would only expect heat entering through the cpu to effect DeltaT(cpu-coolant).
If steady-state I would intepret the enigma as a change in cp/mb Heat imput.
Will post more later. Now going to pub for hair of dog.
EDIT. In the pub I realised that had miscalculated "Heat Removed by Chiller". Have corrected graph