Tell u what, the 6600 ain't made to play current high intensive
graphics game. When u force the older card to play, u actually
stress it. This causes overheating as the card tries to work
harder. If you don't want your 6600 to die, stop playing DMC4. If
you want to play it, u might have to change several parts of your
computer.
To Raraken, the 4870s and 3870s are made to withstand the high
temps (checked from several reviews)