This is exactly how you measure thermal conductivity. What is the rate of BTU/hr across the paste between 2 copper surfaces. You only need to know the thickness of the paste. You know the wattage input. You know copper thermal properties. We know the conductivity of water and air. You can calculate exactly how many BTU you NEED to move, that's the easy part. My 13700K pulls 235w at a full load. That's about 802BTU/hr, just a little more than half of my window air conditioning unit I chill loops with.
Did you watch the video from Gamers Nexus? Are you aware the number can be "tweaked" with unrealistic high temps? You need a bit more than what you are telling us. And how can you know the number isn't simply made up. It's obvious that most big manufacturers like Shin-Etsu, Honeywell, Deepcool, LairD, Dowsil, Akasa are in a moderate range of 5-8 W/mK. Could it be they are more honest and don't use inflationary numbers just for marketing reasons.
And to make it a little more complicated for you thermal impedance/resistance is more telling for most of our use cases but this number can be tweaked as well.
The most important specification is definitely the thermal impedance, which is measured in degrees Kin2 / W. This is an application specific measure of the ratio
the temperature difference between two mating surfaces to the steady-state heat flow through these surfaces. Due to the additional mounting pressure and the size of the area, the
thermal impedance typically decreases while increasing with TIM thickness.
The ability of a material to conduct heat regardless of its thickness is called thermal conductivity and is measured in W/mK. While TIMs can be compared to thermal conductivity values, this value does not indicate how good the material's ability is at minimizing contact resistance.
Choosing the right thermal interface material: paste, pad or foil
Knowing the needs of your application is key to selecting the correct thermal interface materials.
www.mueller-ahlhorn.com
There are two critical thermal performance characteristics:
Thermal Conductivity (TC) and Thermal Resistance (TR). In low bond line applications, thermal resistance dominates performance.
In high bond line applications, thermal conductivity dominates performance. In medium bond line there is a blended influence.
Thermal Interface Materials (TIM)
Nordson EFD thermal interface materials (TIM) provide reliable heat transfer over a longer time than most industrial thermal compounds.
www.nordson.com