As you can see in the photos here, we first dry fitted the heatsink with some white silicon compound on the core, and shim of the R300 to get a good set of marks for milling.

The ATI R300 core doesn't even make contact with the heatsink when a thin layer of silicon-based thermal compound is applied in place of the standard TIM. The thermal compound was applied to the shim (which stands higher than the silicon core) to illustrate where it actually comes in contact with base of the heatsink when installed. The transfer of thermal compound onto the base of the heatsink illustrates just how uneven the cooler even is.

Sadly, this test proved that the extruded heatsink was not even finished well. Extruded heatsinks just about always have somewhat wavy or concave/convex bases so it is important to finish the base with machining or sufficient sanding. While the stock extruded heatsink that ATI package on the Radeon 9700 is sanded to achieve a "better" surface finish, it is apparent that QC is rather lax.

You can see exactly what we mean in the photo above - entire sections of the heatsink do not come in contact with the R300 processor shim. For such an expensive graphics chip, the thermal package is really handicapped by a poor interface. Perhaps a justification of the thick yellow thermal interface material in the first place.

The picture on the left above is what you should see if you remove the heatsink from the videocard. The thick yellow TIM really ought to be thinner over the core of the R300 GPU, but isn't. On the right hand side is the modified stock heatsink.

We removed all the yellow thermal interface material and milled out a shallow area where the shim would have come in contact. With the recess now cut from the base of the heatsink, the heatsink can sit lower, making actual contact with the core. For a further performance gain it would have been wise to even out the flatness of the stock heatsinks's surface finish.