Some Thermal paste or Thermal Interface Material (TIM) is better than others. Some is even made with diamonds.You can find tests that compare them. Overclocking Thermal paste needs to have good heat transfer, but it is also important that it be as thin a layer as possible. The way you do that is to sand the CPU cover as flat as possible using finer and finer grades of snadpaper on a peice of glass. Good quality heatsinks will already have a nirror finish and might even be slightly convex to press down where the CPU cores are. But heatsinks can be "lpped" this way also. This produces almost a metal to metal contact with room for very little TIM.