Today was displayport day. I might be imagining, but seems the picture quality is just slightly better than HDMI. BUT, still occasionally goes black for that one or two seconds. Always returns. Has not "lost signal" in several months as it once did the third or fourth time the monitor went blank. It would then report "no hdmi signal found" or similar. Would require reboot. Sometimes just switching inputs on the monitor for a minute then back.
So, not DP vs HDMI. Not cable.. Likely not monitor on 2 different inputs. Leaves driver or dock. I am on the latest Intel driver as the later Lenovo drivers have issues (memory leak in DWM. Exe).
I rarely use the NVIDIA GPU and have things set to let windows decide AND the intense apps like Lightroom and even browser set to power saving mode. I guess its possible the blanking is Optimus trying to switch drivers. Maybe next set of experiments.