Well, there's also sth called spreadability and filling ratio (how fine the thing is) and AC is supposedly better.
AS5 may be better with physical properties (thermal conductivity) but application is a different ball game alltogether.
If it was better to ommit TIM in your cooling assy then nobody would be using it by now!
Direct metal-to-cilicone contact without TIM is laughable in terms of thermal transfer compared to the same thing used with TIM.
You may want to use mercury but I doubt you'd survive t tell the story
