Here's a very logical and proven explanation why you may not show a
lower temp with better/silver greases.
First of all, nothing changes the heat flow/power dissipation of the cpu except the cpu itself and app/s running...And all heat generated is removed, but higher thermal resistance cooling systems force temp in cpu to rise in order to force the heat out, as "Temp drop" is the motive force in heat transfer. Cpu temp rises until heat out equals heat generated...that's the physics.
But the cpu/hs heat transfer path has several components with their individual thermal resistances, and yes, the silver grease lowers the
"overall" resistance, and it therefore lowers the cpu internal temp and the cpu case top temp on the cpu side of the lower resistance silver grease interface.
But it "does not" lower the hs resistance. So for the same heat transfer, any sensor measuring hs surface or related temp will "not be lower". In fact, it will be slightly WARMER, because the lower resistance of the hs interface causes a bit more heat to flow thru the hs rather than thru the constant resistance path of the pins...a minor "secondary/negative feedback effect".
Hope it's clear now that you can't measure the effectiveness of an interface material UNLESS you can measure the temp on the cpu side of the interface...which is a practical impossibility for most cases.
Like real estate..."location" is everything.
You could try eading internal thermal diodes on Intel chips, as they are on the cpu side of interface. Diodes are not "accurate", but they are "repeatable"...ie, tell same lies every day.
John C.