I wouldnt recommend modding your radeon 8500 and trying to risk destroying it in any way.
Look at the extreme overclocking results here =>
@ 320/700
They are nothing to write home about. You absolutely will not notice the performance improvement in any new game with this card. Even in DX8 games you wont. This card is too slow. You'd need 1000mhz GPU and 2000mhz memory clock speeds to compensate for 128-bit memory bus and 4x1 pixel pipelines and 2 vertex engines.
BTW, I score 11500 with it at 275/275 on P4 2.6@3.2ghz what you get with that A64 rig?