To the original poster, and I apologise if this has already been suggested - I haven't read the whole thread.
I have an ATI 4850, and with it I have no real issues with BS - But, when I play Crysis it seems to cook my graphics card if i don't increase the fan speed to 95% from the 60% default which is sufficent for every other game. This results in my computer locking up... Now it is a different graphics card, and a different game, but it might be worth looking into.