I do a lot of system building and have tested a number of thermal grease, pads and thermal tapes. What if I told you that it is all hype? So long as you have something that is thermally conductive, any thermal grease will do, do not let anyone persuade you otherwise.
The best grease is the least expensive. Here’s a search term. If you paid more than $8 or 8EU, you got ripped off.
There’s a ton of entertaining YouTube videos on the topic of using everything from Peanut butter to toothpaste to chocolate as a thermally conductive barrier between overclocked CPUs and their respective heat sinks. If you look at some of the results, there’s less than a 3-5c difference in thermal conductivity which for 3D printing is close enough. https://www.youtube.com/results?search_query=PEANUT+BUTTER+as+THERMAL+PASTE
NOTE: I’m not suggesting using peanut butter. 