I think most efficiency gains from the architecture during max constant load on the GPU without throttling is eaten by relatively high clocks compared to GK110, because they need it to up the performance appreciably. What needs to be clarified is that this scenario doesn't happen during ordinary gaming loads so it's only slightly relevant for a mid-range chip which is not a compute chip, not with such an abysmal dp performance. Teslas will most likely only use big Maxwell. If it can get better battery life during gaming loads then it's a success from efficiency POV. The chip is much smaller to make it appreciably faster they really need those high clocks. At lower clocks and voltages it would draw less power than GK110.