I just installed a FirePro W2100 to use with my LG 34UC97 (3440x1440) monitor, and just about every time the system wakes up from sleep, it tells me that there has been a problem with the DisplayPort connection that "prevents me from using the highest resolutions and/or refresh rates". The display runs at 30 Hz after that, instead of 60. I can force it back to 60 with little effort through the control center.
The monitor is DisplayPort 1.1 by default and can be set to 1.2; I tried both modes with the same results. Using the on-board Intel HD Graphics 530, via the same DisplayPort cable, there have never been any issues (at least of this kind, hence the FirePro).
According to its specs, the W2100 can run 3840x2160 at 60 Hz, so why should it have a problem with 3440x1440?