1) Absolutely incorrect. I have done extensive work with YACoin, which is currently at N=14. If you know what to look for in a card and how to work with it, the GPU is extremely more efficient. My findings are out there if you do your research. If you can't find it, the summary is : 2.9 KH/sec with a GPU consuming 25watts - compare that to any cpu and it favors pretty well.
2) That's a poor comparison from the page. What is unfortunately missing from that page is the amount of memory the card has - this is the most important aspect of how the card will perform at N=14. I've put that info into many of the entries I've posted, but I'm not the only contributor. The Xeon you quoted is actually mine, and it is horribly inefficient! To get that, the server is running at over 400 watts, and I get a whole 1.53KH/sec (at idle it's over 260Watts), but I only get 1 miner out of it! With a GPU mining machine, I can run 4 cards giving 10+ KH/sec for 200 Watts. Actually, if you following cudaminer, the nvidia 750ti has come along and is now getting over 3 KH/sec for < 60Watts too.
3)Finally, something I agree with
To point 1 and 2 above; yes I had not noticed the higher efficiency on the comparison page. I do not ever intend to provide improper information. Another found and posted right below me (Puycheval), the R7 250 was doing 2.47 kh/s @ 35w. It would seem then an N = 15 would possibly be the last GPU point. However, even at 14 it seems there are only 1 or 2 GPU's that are efficient?