I totally agree.
I've gotten the Aavid Ultrastick phase-change goop down to what I thought was about 1-2mils after clamping. It flowed like water when hot but never got any thinner than that. And that's with belleville washers, etc.
The grease I'm using now starts at that thickness (if I put it on with care) and then just gets thinner with pressure. Their thermal conductivity specs are pretty close so I'm going with the grease.
I'm using the Wakefield 126 Series stuff now but Dow TC-5022 looks great. Several times the conductivity of the 340 grease. I have a sample on order and will see if there's any difference. At these thicknesses though, I can probably use mayonnaise and still be OK. :-)
John