Are you saying that you want to increase the voltage on your cpu in order to overclock your gpu?
They are two seperate components and you have to approach each one seperatly. Now that you have your cpu overclocked and stable at 4.4 ghz you will have to overclock your gpu to see what settings you will need to get to the frequency that you want. They are not connected and you will have to adjust the voltage on the video card to get your overclock to your 20%. Every gpu is different even though people may have the same model there are microscopic differences that will make each persons gpu overclock differently. The only way to see is to do your overclock and see what you end up with.