I've used the latest build some and it seems to be easier on the eye than Windows 7 for 4K. Can't compare to 8.1 as I never used that. Thought I had a workable solution on 7 until I tried 10--so many more things can be adjusted. Had more trouble with audio than video honestly. Finally got some drivers to work. MS hasn't released video drivers yet for the newest version of 10 so all are hoping it will be better still. I got a pretty old version of Nvidia graphics through Windows Update but it tended to work better than the 8.1 drivers I tried from Nvidia. For now a lot of the drivers have to come from MS since nobody really has working drivers or compatibility with 10. Part of the reason for the tech preview is for folks to let MS know what works and what doesn't so they can work out
fixes--seems they recognize what hardware is in the machine and then try to pass along the best solutions through Windows Update. Graphics drivers are expected to release in the next week or so I think.