Overclock Sapphire ATI Radeon HD 4350 512MB Quiet

Just recently i see a forum which does overclock exceed the AMD OverDrive, 650/475. with Sapphire TriXX latest version, my graphic boost about (780-600=180MHz) with Memory clock of 477MHz with default voltage (voltage cannot be changed. thats weird). anyway, when i go beyond 780MHz, i start MSI Kombustor 2.3, set 1280x720, no AA with openGl 2, my screen goes grey. i cant do nothing so i restart it. them,, my max is 780MHz for gpu. for the memory, i want to overclock above 500MHz but it shows artifacts when goes beyond 480MHz. i wonder why others can overclock memory clock beyond the 500MHz with stock voltage?

Everything just fine when running NFS Shift 2. just 15% speed up from previous clock (650/475) to current clock (780/477). it shows around 25-30fps with fraps when playing with 848x480(thats dump), noAA, highest setting to all except shadow in low, motion blur to disable (or no), reflection quality to medium (i cannot put to high. the game crash. never happen before but after install RadeonPro) and vertical sync to off.
played with 1280x720 with same setting, my fps goes almost half (15-20) the previous resolution.

My system is AMD Sempron 140 overclock to 3.48GHz (i know its require at least tri-core), ram is Kingston 2GB DDR2-800 single channel (overclock to 860MHz), chipset is NVidia GeForce 7025.

my gpu status when stressing with MSI Kombustor, set to OpenGL 2, 1280x720 no AA windowed, fps is 7 fps (average). temp is at max 60 celcius. at idle, around 45-50. this graphic card is fanless so i use usb fan table to blow it (traditional but effective). i know im "crazy" but this is the choice i have for now.
later, want to try GTR evolution with max setting.

well, quite satisfy for me... for you?