Somewhat unrelated, but maybe you can shoot me down since you seem to have some experience?
Metal is an incredibly good conductor on its own, and the properties of thermal paste (typically) are just barely better than air. So long as your cpu and heatsink are fairly flat surfaces and mashed together physically, it seems like either forgoing or having the absolute minimum amount of paste is ideal. I've used a razor to leave an absolutely minimal layer of paste (e.g. filling in sub-millimeter surface structure) on my latest build, and cpu temperatures are well within a reasonable range. But I'm also not trying to OC the cpu or anything.
>...and the properties of thermal paste (typically) are just barely better than air.
I am not certain how you have managed to come to such a conclusion. Thermal conductivity of air is around 0.03W/(m·K)[0]. Good thermal, non-conductive paste is like 12.5W/(m·K)[1] (or 400 times better than air). Conductive ones are in the region of ~40-80 W/(m·K) and Aluminium is 237W/(m·K). Also air also expands pushing the cooler and CPU away.
Normally you if choose between "too much" and "too little" paste, you pick the former. The pressure pushes out the unneeded amounts.
Don't, you need to multiply the raw conductivity by the linear distance occupied by the thermal paste? I presume that distance will be at least two orders of magnitude larger than that occupied by air in a metal contact only setup.
I would be extremely surprised if increased pressure due to air at higher temperature played any role whatsoever unless the bolts connecting the heatsink and cpu were very loose. If anything, I'd expect the increased conductivity of air at higher temperatures to dominate.
I'd also expect there to be effects at the metal-paste and paste-metal interfaces which reduce the effective system conductivity (i.e. phonons are much more likely to reflect in this scenario than in a metal-metal interface).
It's very impractical/expensive for mass products to make the surfaces in question so flat that no thermal paste would be needed. Many tests and reviews have been done. Even if top-of-the-line coolers came with perfectly flat surfaces, Intel's heatspreader is not -- otherwise it would cost so much more. Also, heatsinks can be applied with a lot of force, which usually pushes out the "unneeded" part of the thermal paste. In a bind, even lipstick, toothpaste, chocolate and other silly compounds work better than nothing, so I'm not surprised that you're getting ok results even with a touch of thermal paste.
A fun thing to try is using a modern low-end CPU (latest i3s, Pentiums, Celerons) without its cooler. Not advised by Intel, of course, but you might get into your OS of choice even before it starts throttling. I'm somewhat comforted by the fact that a CPU automatically powers of once it reaches something above 100 C (103 maybe?) and throttles a few degrees before that. Those temperatures shouldn't leave the silicon damaged.
In practice, thermal paste is a must. If you don't like those (I personally don't, they get everywhere by accident and can be tough to remove), try getting an IC Graphite Thermal Pad which is reusable and rivals really good, if not the best thermals pastes, according to the limited number of reviews I've seen. I think that its practicality beats better results in non-highest-end applications.
Its really not that hard to create flat surfaces- anyone with a lathe, a hard cutting instrument, and a bit of fine grinding material can probably get a contact bond between two pieces of metal.
Metal is an incredibly good conductor on its own, and the properties of thermal paste (typically) are just barely better than air. So long as your cpu and heatsink are fairly flat surfaces and mashed together physically, it seems like either forgoing or having the absolute minimum amount of paste is ideal. I've used a razor to leave an absolutely minimal layer of paste (e.g. filling in sub-millimeter surface structure) on my latest build, and cpu temperatures are well within a reasonable range. But I'm also not trying to OC the cpu or anything.
Thoughts?