The overlapping view here shows well where all the problem spots are on the Athlon's 'heat spreader'.

Solution:

In one word: lapping. If you are serious about eeking out the most performance from your Athlon, and want to use the Athlons' heatspreader rather then a direct-to-die configuration, lap that puppy. The heatspreader that is. the plate can be removed from the rest of the processor fairly easily and sanded and polished to a perfectly flat and super-smooth surface in a half hour or so. This is best done by using 400, 600, or 1500 grit automotive sandpaper, a very flat surface (like a glass table, or granite counter top), and a bit of water. I've found that moving the object around in a figure-8 pattern yields the best finish.

If a cold plate is to be attached, it will appreciate the time and effort put into making its home the most ideal for thermal transfer. If however, you are content with using a standard heatsink, the stepped base design variety offers the most compatibility with unflat heatspreaders of this type. If a full contact (heatsink makes contact from one edge to another) type heatsink is being used, lap the plate. Even if only the high spots are removed, it will be better for it, less thermal goo will be needed so more heat will be moving away from the cpu, and hopefully cooler operating temperatures will lead to better overclocking results.