Hmm, how so. Forgive my ignorance, shim on an ATI?

The R3x0 and RV3x0 radeons have a thin shim around the edge of the GPU. This prevents the core being crushed by the heatsink during manufacture. The core is exposed like with the athlon XP. The problem is it also prevents a very firm contact between the GPU and the heatsink. Some people remove them but its risky. With better heatsink contact even the 9700non pros can hit 400mhz + sometimes.

Ah, gotcha. In all my wanderings, I have never seen the HSF removed from a Radeon. Thanks for the info. :)