Actually tried my ebay bios modded visiontek hd4850 on another motherboard. Stable no artifacts 3dmark06 and Vantage. Bios set 725/1125. Fan set to idle mid 50's and not get past 65 load. Works with CCC 8.7, haven't tried 8.8.
For you guys to play with if you want.

Custom hd4850 bios 725/1125 fan 55-65 c.
http://rapidshare.com/files/139289043/RV770.bin