Well my R4830 is running at
GPU - 685
Mem -1125
That is max what can run trough 3dmark06 without error or glitches 3 times. Max temp is about 61-62 Celsius and I am using AMD Gpu tool
It can work on 700 Mhz core, but hang on SM 2.0 test in 3dmark06, but no problems with SM 3.0 test.