Hi, I have just bought 2 X Samsung 28 Inch 4K's for use with my 2013 Mac Pro 6 core D700 and I have to say I am rather disappointed by the performance of the monitor, I was waiting until today for Minidisplayport to display port cables to arrive and I hooked it up, the monitor runs at 60hz but I am seeing choppy video playback with lots of frame dropping. I have tried various test videos, 4K and 1080 60p and 30p, full screen and in windows but I just can't get smooth video playback on this Samsung monitor, I also have my old iMac connected in target display mode, when I drag a video window over to the iMac it runs smoothly, when I drag the window onto the Samsung 4K it drops frames and the playback is choppy. I have tried the various settings on the monitor, i.e.: Response time, standard, faster, fastest and actually it gets worse with it set to faster or fastest. The frame dropping is SLIGHTLY less if I expand a video window to full screen but any video playback is choppy and dropping frames, especially when it's a smaller window. Anyone else experienced this please? It's like there is either too slow a screen refresh to keep up with video playback or it's like a little buffer is getting full and stuttering playback. I like the monitor apart from this and the very critical sharpness setting so I hope there is a fix so I don't have to return the monitors . . . . Thanks!