I don't post often but I've been around for a while.
So just got one of these and I also have a PG278Q (which I just RMAed and have to pickup the replacement for which arrived at my office).
The PG279Q I got has no apparent defects, I can't see any lightbleed (at least nothing like you see on smartphones and tablets), there is some glow when you have a totally dark background.
My opinion, very nice colors, feels like higher definition than PG278q alsmot. Very uniform image all over the screen, for sure it shows IPS is in another league as far as image quality.
I consider myself to being very sensitive to input lag, motion etc. I definitely feel like the PG279Q is laggier than the PG278Q, not in the input lag but on how smooth the motion appears on the screen. I feel that when you move your mouse, the speed is there, it tracks nicely the mouse movement, but the image is blurrier than on the PG278Q.
So for now, totally sold on the better image quality but not so sure about gaming performance if you are very sensitive to motion quickness/smoothness.
I'll have to try some more.