There is an article over at Rage3D that
compares various Radeon 8500 bios files.
Some revisions have more aggressive
memory timings, but are not appropiate
for all 8500s due to slight differences
in memory chips. I have one of the
later 8500 revisions with the smaller square
memory (forget the name) versus the regtangular
chips with the pins coming out the side. My card
will overclock to about 312/312 consistently
with stock cooling (i never run async).
http://www.rage3d.com/articles/8500bios/billchase