There are a few factors that determine a heatsink's cooling performance; the heatsink itself of course, the thermal interface material, and the factor most people forget, flatness of the heatsink base.
I've always lapped my own heatsinks with 2000 grit sandpaper, sanding till I got a mirror finish. Nice to see a lapping kit out there with everything you need to get a great lap job done.
Check it out here - Easy lapping kit
Lapping makes for a better chance of getting a great and even contact with your CPU die or heat spreader, I personally have always noticed temperatures drop by several degrees just by lapping a heatsink, even brand new ones.
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