Little update from mvktech:
I had a member there, saw1971, make a BIOS of my ASUS DC2O GTX680 with a max voltage of 1.27v just to see if it might work..
Well, it didn't.
So, there's either a hardmod required or there are parts in the BIOS that limit the voltage. Some sort of security or w/e.
BIOS does appear stable, and strangely enough setting 1.27v in the BIOS allowed for noticably lower vdrop and 15Mhz more on the core even thought this can be completely unrelated to this change.
With 1.212v I usually got 1.207v with light / no load and 1.188v with max load.
With 1.27v in the BIOS this is 1.211v idle and 1.193-1.198v under max load.
I can now run 1215Mhz boost with 1800Mhz VRAM on my very badly binned 680.