Power consumption, plus PiFast
Intel's improved the overall power-draw of the X79 platform when compared to X58. Even so, it's put in the shade by a Core i5 2500K chip sat on top of a Z68 board.
The Extreme 4 pulls an additional 10W over the ASUS offering. We double-checked the voltage applied in BIOS and the ASRock's VID is smidge higher, helping explain these results. Again, the under-load figures are good for a six-core, 12-thread chip, all things considered.
Moving on to apps, the high clockspeed of the 3930K pushes it to first place. There is no performance difference between X79 boards.