I O.C my HD4850 from 625/993 to 700/1098 with ATi Catalyst Overdrive.. The test result was 'passed'... but when running FarCry2 at 1920x1080 BSOD appears(GPU stops responding)... which other O.C software would be better to attain stable clock..
ok, to let you on a little fact, the ati overdrive thing that "tests" the GPUs is totally BS
it said i could overclock my 3870s with a core clock of 890mhz and 1375mhz mem clock!!!!
I personally just know what my cards can handle from the pains of crash reports and GPU not responding reports. im sure there are some good softwares out there that let you test out your OCed settings but i dont use any.
he only sure fire way to make sure it is stable is to play your favourite games.. If it crashes then back off the OC a bit and try again. There is so software that could find every instability, though any benchmark utility will give you some idea of the stability.