If you're expecting big performance differential between motherboards with shared chipsets at stock clock, you're setting yourself up for disappointment.
Of course, that's just dandy for the Asus P8Z68-V LX. It's main selling point is cheapness.
So all it need do is match the the performance pricier boards to be a winner. Which it most definitely does.
Also intriguing is the comparison with an X79 board and six cores. In real-world applications with mixed work loads, such as Photoshop, the difference isn't dramatic.
CPU rendering performance
Video encoding performance
Real-world productivity performance