All I can suggest is build a hot rod of each type and see it in action for yourself. I have built a couple dozen dropins and several dozen lights with threaded pills. It does make a difference.
In practice, threaded pill setups are easy/reliable to get an 80% solution to thermal transfer. The contact area is about the same as a straight, tight-slip-fit pill, but the contact pressure is way higher with threaded setups in almost every instance except precision machined and machine pressed drop-ins (which kills the main selling point of them in the first place). CTE is another thing to consider. If your host expands a higher percentage per degree than your drop-in, then it actually would loosen up in operation. Of course the opposite is true as well, and could be the best argument/approach at creating a good heat path in a drop-in setup.