In case you didn't notice GFX cards are overvolted by manufacturer. For example.
My GTX 560 Phantom, that I was forced to return because my PSU was overheating (top position in case and I repaired it with low speed fan), had 1 V for normal work.
My GTX 660 Can do 980 MHz on 1.05 V, and it's stable in overclock at 1.085 V. Of course manufacturer overvolted it in boost to 1.175 V which kills overclock and causes lower speed when overclocked. Yes I can kill power limits by flashing BIOS. 40 nm card used less voltage and was completely stable and had massive overclocking headroom, vs 28 nm card which is faster, but it has much less overclocking headroom (and asymetric RAM).
Well. If 290x would run at 1.2 V, it runs at extra voltage already. Properly designed 28nm card should use 0.95 - 1V.