"...as resolution increases, the relative usefulness of increased memory bandwidth also increases. Although the effect of doubling resolution does not quite result in a doubling of the bandwidth scaling, it's actually surprisingly close.
I would also add that number like 57% bandwidth scaling is incredibly high relative to most cards, and pretty damn solid evidence that the Kepler offerings came out with less memory bandwidth than they probably really should have. And if you AREN'T overclocking your memory because you've always heard it 'doesn't do much', well ... with Kepler ... it does A LOT."
-http://www.overclock.net/t/1364927/so-how-much-does-more-memory-bandwidth-actually-help-at-higher-resolutions