1. Windows 10 supports newer graphics cards much better with newer revisions of WDDM (more efficient, higher top-end performance)
2. Multi-monitor taskbar management is a lot more flexible and useful on Windows 10 - you can have multiple taskbars, and either copy all your taskbar icons for windows across each monitor or separate them as you prefer
3. Scaling of the OS on high DPI monitors is way, way better -- to change it you don't have to log off your system, and the quality and performance of the scaling is better and more consistent across apps with different UIs