Problem with Xstar-DP2710LED

[ToastyX]

The problem is your monitor can't handle higher refresh rates without uniformity problems. That darkening is a common artifact when overclocking the QNIX/X-Star monitors, although some units are better than others. Reducing the horizontal total to 2652 might help a little, but if it's happening at 90 Hz, then there's no way to avoid it at higher refresh rates. There's nothing else you can do except try another unit and hope that one is better.