I played with some 99% isopropanol and some IC7 (which, according to the label, "Contains 92% diamond by weight"). The tubes are the original revision (I bought them within a few months of release), which supposedly is thicker than more recent stuff... combined with the fact they've just been sitting in my bin'o'TIM for awhile, this paste is about as thick as it gets. It might even make do as a high performance thermal pad for thicker gap.

The paste, with a little bit of mechanical mixing, thins well in alcohol. I didn't test it's performance, but thinned out sufficiently, it spread really well under pressure (I used a flat piece of glass on top of a heatsink and watched it spread)

I tried a test on a rougher heatsink, first with just a water drop, then with some thinned AS Ceramique (which was harder to mix, BTW), and sure enough, the liquids followed the grooves, leading to an uneven application. Furthermore, after the alcohol burns off, the paste would probably decrease in volume enough in the valleys that performance would be compromised. That's the theory, anyway.

So, assuming a well finished AND flat surface (on both interfaces), I think thinning pastes may be the way to go for maximizing performance. Due to the very quick burn-off time, it's not practical for TIM companies to use alcohol as a carrier substance, so we'd have to thin it during the actual application time, and even then, work quickly. Due to IC7's low percentage of carrier substances, I think it makes an excellent test subject
for "thinning".

I use the word thinning carefully though, as it's all about temporarily suspending the best performing materials (be it diamond or metal or some ceramic or whatever) so that they flow into all the tiny crevices, rather than dissolve any existing carrier substances (which may be a side benefit, but it does complicate mixing, as shown by the more difficult to mix Ceramique). ie Temporiarily replacing the existing carrier substances, rather than improve them. (Maybe super fine diamond powder in pure alcohol is best then?)

So, anyone care to test any of these theories? I don't have the equipment to do it myself.

Sidenote: it's hard to work with out of the tube, but slightly thinned, IC7 DOES make an excellent metal polish (shined up a few heatsinks really nice)