First, the person comparing the GTX 680 to a GTX 670 and coming to the conclusion that the PS4 and Xbox One would have a similar disparity in performance because of the difference in teraflops is wrong. The GTX 680 and GTX 670 are based off of the same GK104 chip so everything on these chips are exactly the same except the core clock and the texture units/stream processors. The PS4's GPU on the other hand is based of off "Pitcairn" which is the chip used in HD 7850/7870s while the Xbox One's GPU is based off of "Bonaire" which is a chip used in the HD 7790s. So what does that mean in layman's terms? The chip used as a reference for the Xbox One's GPU is a mainstream part while the chip used in the PS4 is part of the enthusiast class GPUs.
To get a better understanding of the disparity in power here, take a look at Anandtech's fantastic benchmark suite: http://www.anandtech.com/bench/Product/776?vs=857
If you take a look at those benchmarks, it looks like the PS4 GPU is significantly more powerful. The comparable GPUs found in PCs show a 10-15 FPS lead over the other. And it makes sense. The PS4 has twice the fillrate power and 50% more raw shading performance. Should be a no brainer.