I have the idea that its the same with the 5850 and the 5870. My 5850 with 5850 bios would only run 900-1125. I know the 5870 upps the core voltage. But my memory also saw a boost. After the 5870 bios i could do 950-1225. So there is a chance that the 5850 bios also uses the lower memory voltage like the 5970 at default. This might make it more easy to find out. I understand your problem that without a 5850 you cant realy test it. I hope you get enough donations to buy one Its not that easy. With the X1800, X1900 and X1950 its different. From day one there where tools that could change: GPu, Mem and Mem I/O voltage. I dont know why but i think AMD wanted to do something special for the OC people. But this might be something that w1zzard knows. Because ATi Tool had support for those things. So because your 1950 can it does not mean the others can aswell. They might because on the HD4 and HD5 there is a digital PWM for the memory. In that case you get the problem where BAGZZlash was talking about. Try to find out how the bios controlls it.