You’re doing it the dangerous way.
Generally you start with your stock Voltage and clock speeds and step them up as needed SLOWLY.
1. Up mhz by 30-50 if stable do again.
2. If unstable up voltage VERY SLIGHTLY until stable.
3. if temp is ok start at 1 again
you may not succeed in getting to 1ghz core but if your not carefull you will succeed in creating an expensive paperweight.
I agree with you, because actually you dont need that much of voltage to be provided to your Graphics card.
If you can increase 30-50mhz without increase in voltage, then why not? Its logical.
Finally it will end up by getting too hot, or extra voltage may damage your GPU, and you'll have no other option except to use it as a paperweight..!
Sometimes excitement kills your thinking power, and you end up achieving literally 'NOTHING'..!!