I used the program Nibitor to edit the bios at my Sparkle 6600 (standard GPU 300 Mem 500).
I increased the clock to 500, mem to 600 and I activated the temperature monitoring (it was disabled).
Then saved to a file and with a program called Nvflash - I downloaded it in ISO format then I put it on a floppy disk and added the modified bios file.
After that I boot form floppy disk and "updated" the bios.
:!: If you are not familiar with those things DO NOT DO THIS. You could PERMANENTLY DAMAGE your video card. However if you are and you do this you can modify most setings for and save them to bios - more driver level overclocking.
:idea: You can do a hard moding to - increasing the voltage but I do not have the know how (this is to much for me) - DANGER