UPDATE: have tested the replacement CPU and it is cooler than the one it replaced.
I replicated the retailers test above at 4x 4.4 GHz turbo, other settings at default and got slightly cooler results with the Noctua NH-L12.
I ran an OCCT test with the same setup and whereas previously it would overheat and shut down within 2 mins at lower settings necessitating an underclock in earlier tests, this time it completed without problems.
So clearly there was more heat being retained and or generated by the original CPU. I can feel it in the heatsink in fact, more heat is being dumped into the heatsink by the replacement CPU and the HS is getting warmer as a result, suggesting the thermal interface might have been the cause of some of the first CPU's overheating. However there is also much lower steadier power draw with the properly cooled CPU. A hot CPU will draw more power but a power hungry CPU will get hotter, which is the root of the high transient power draws I observed in the overheating CPU I don't know.