I've been watching this thread for a while now ever since I received my PB287Q and decided to chime in on my experiences.
I, too, tried to use the monitor with a 290x and have been seeing the same issues. Setting the refresh rate to 60hz will cause the screen to flicker and turn off repeatedly on desktop but isn't too bad when actually playing a game.
After a couple days, I decided to get a replacement but I'm seeing the same issues on the second monitor. It's actually a lot worse. The monitor tends to just remain on a black screen whenever I try to set it to 60hz.
All the flickering occurred mostly while on Windows but I did see it occasionally while on the BIOS.
Since I know now that this is most likely AMD card/driver related, I'm probably just going to sell my 290x and go with the 780 TI.