The 9400gt isn't a overclockers choice but you can focus on the shader when overclocking the card for performance reason alongside with the vram. Don't bother with the core clock as it will limit the peak clocks for the shader but it doesn't buy much headroom though. If you are using afterburner you might not be able to do this but if you are using Riva Tuner then you might get up to 1.8ghz on the shader before crapping out. The vram isn't going to be kind when overclocking if the card is a GDDR2 based knowing that they don't reach no more than 425-550mhz range (physical clocks not the data rate). Cooling is ok but just be sure to keep the thing clean.