yes it's definately possible. I think what you have to do is download the omega drivers to unlock the extra 4 pipelines on the card. Seems that people are saying the powercolor 9800se is overclocking the best. Other cards are more likely to have artifacts after unlocking the 4 pipelines I'm guessing.
it is possible.. but anything OCed can cause problems with the video card.. and it will not last as long as a card that is not OCed. You also need to put a better fan on the VPU as well.