I modify the rom in a hex editor and change the voltage entirely.
In other words, i do not change the dpm tables, i just lower the entire voltage by -100mV (for example) so that the controller itself will automatically give the voltage that is needed.
In this case, a specific clock won't give you issues as the controller will adjust voltage for what is needed.
I saw your XFX mod. You used 800 instead of 900 in the original BIOS. I tried your mod, but it does not change the voltage of the core at all.
Are you still working on that?