I managed to work some magic on the visiontek 4850 512mb bios, unlocked 800 core / 1300 memory limits in overdrive and it passes digital signature ;) etc It works with all drivers....Nothing else is modified.
It may work with other reference version cards........I am working on higher but atm it does not work with all drivers.
You will most certainly need volt mods for higher clocks as well as better cooling....
Usual disclaimer applies
***Flashing a modded bios to your video card voids warranty as does overclocking. You choose to use this at your own risk and I will not be held responsible, nor will ATI,AMD or visiontek***
http://members.cox.net/nfridenti/test1.bin rename to .rom where applicable......
Shot of it working with driver version ( 8.12 ) and Overdrive.
http://members.cox.net/nfridenti/test1works.JPG