Power consumption for the GTX 780 Ti SC ACX is slightly higher (15W to 30W) compared to the reference GTX 780 Ti. However higher power consumption is due to high factory GPU overclock, but for that you get better performance. Overall, performance-per-watt is still good. Recent Geforce cards tend to consume 10 to 40 watts less than competing Radeon cards in a multi-monitor scenario.
